OK. I’m just doing the “cover at least the cost of the plate” gift, which was at least at one time standard wedding etiquette (at least so far as advice columnists, Miss Manners, and family tradition have led me to believe). Perhaps this is not the case anymore.
This sounds completely bizarre to me. I give gifts based on my relationship with the couple in question and what I think they might need, not how much they spent on my ticket to their party. Besides, as olives said, that young couple scrimping to throw a party at the VFW needs my gift far more than the fancy-pants $50k, silver spoons party couple.
Our wedding was about celebrating our union in the company of friends, not about the payoff we’d get from our guests, and I think it’s wretched to imagine it so. We had been living together for several years, and though our home was furnished from yard sales and second-hand stores, it was furnished, and as such I didn’t really expect gifts, because we didn’t need things the way a couple does setting up housekeeping for the first time.
As it turned out, we got some very nice things and a bit of cash, which was nice, but we’d have been equally blissful if we hadn’t gotten a dime. For what it’s worth, this is the first I’ve ever heard of basing your gift on your perception of the cost of the meal.
Oh, I’m not disputing that–just saying it sounds bizarre to me. Maybe it’s different when you’re likely to be invited to a lot of weddings as a society thing with couples with whom you may not be terribly close? I’ve only ever been to a few weddings, and they’ve all been very close friends, so I’ve been fortunate to be able to give them meaningful, personal gifts rather than just picking something off a registry. On the other hand, I’m not the sort to get invited to, or to attend, weddings when I’m not close with the couple in question–I’d feel like I was being invited for… well… the expected gift. 
Says who? The VFW couple might just be a low-key couple that could well pay for a $30K but is philosophically opposed to it (as many here.)
It’s not bizarre to me at all. Let me put it to you this way: I want to give my friends a net gift of $100. If my friends are having the shindig at a backyard barbecue, I might give 'em $120. If they’re doing it up and having a gala at The Museum of Contemporary Art, I might give them $175-$200, so they still end up with a $100 gift after I allay some of their expenses.
Right. Which is why, if I knew the couple well enough to attend their wedding, I’d likely have some idea what they want or need. Additionally, if I’m good enough friends with someone to give them a $200 wedding gift, I’m good enough friends with them to give them a $200 wedding gift, whether they choose throw a low-key VFW party or a million-dollar bash.
ETA: that explanation makes sense, thanks. 
I should add. That said, a couple should not expect their guests to offset the cost of an expensive reception, just because the couple decides to choose to have an expensive wedding. I’m just saying what rules I follow as a guest, but if I couldn’t afford it, I wouldn’t feel at all guilty about leaving only $50.
Our wedding cost around $1000 in 1988, including dress, food, flowers, officiant, organist, and DJ. The wedding was at a church and the reception was in my sister’s union hall, which could be reserved by members for free. The flowers were done by a friend of mine as a gift(we paid for the materials), my cake-decorating sister made our traditional wedding cake and did a beautiful job (again as a gift), my mom and caterer sister and BIL prepared the food (we paid for the food; the work was a gift), and a friend of my husband’s did the photos (he was not a professional and that was probably the only thing I have regretted, but we have photos from family of the reception).
My dress came from JC Penney for about $150 and my crafty sister made a picture hat with satin ribbon for me to wear. My husband rented a tux and we asked our ushers and best man to wear a suit. My niece was my only attendant and she wore a beautiful black dress that I had previously worn in my friend’s wedding. Our wedding rings were plain white gold bands purchased in a 2/$60 sale.
The largest expense, besides food, was the DJ at $50/hr and that was partially because when his time was up, our friends who wanted to party longer took up a collection to pay him for an extra two hours. We had around 100 people there and everyone had a great time.
$4000 in 1995.
It was my second wedding, and Brainiac4 wasn’t big on the big wedding thing. So the wedding itself was ten minutes in judges chambers with six guests.
We had 100 people at a reception and served sub sandwiches, pop and beer. I made my own cake. One of my girlfriends did my flowers. My dress was an off the rack cocktail dress for under $100. My husband got a new suit. The reception hall was the biggest cost - it was $1000 just to rent the place we had. We didn’t have a photographer. My mother worked for a party house, so the decorations were almost free. We did pay for a DJ for $500.
And it was still $4,000 by the time we were done. Even doing it cheap the little stuff adds up fast.
(Friends got married on a Tuesday night - you won’t believe the bargains to be had if you get married on a Tuesday. His family had four generations that had been married on the same date - and they didn’t want to wait five years for that date to fall on a Friday or a Saturday.)
Having the reception in an old rented theatre sounds like a lot of fun. I don’t think I’d show a movie at my wedding reception, though, especially if you want people to dance and rock out - it would really drag the reception down, in my opinion. I discovered this summer that you want to do what makes sense to you, but you kind of have to keep your guests in mind, too. We went to a wedding where they had a cailegh dance, and it was not fun at all for us. Nobody knew how to dance any of the special dances, and it was, frankly, quite boring, sitting and watching a couple of people who knew the dances dance, while everyone else who wanted to dance just kind of waiting until the formal dancing was over.
(And don’t let your SIL see any more dress pictures - or send her ones you don’t like, to mislead her. What kind of person buys a dress that someone else has said they love and might buy?)