Someone asked why I thought it was kinda inconsiderate to invite someone without a guest. Of course, I can imagine all kinds of different situations. But at the heart of my thought were my impressions of hospitality.
Speaking in generalities, I generally think invitations should be as free of conditions as possible. For example, one generally oughtn’t invite someone into their home, and expect to dictate that the behave in a manner other than what is natural/confortable to them.
With weddings, different groups are often getting thrown together - each party’s family, and friends they made at various points in their lives. Some people will travel a distance, and incur considerable expense to participate. I do not have difficulty imagining circumstances where an invitee would be more comfortable and would enjoy the experience more if they were able to travel and attend with a companion.
IMO, the bride and groom are hosts. And as a host, my aim is to make my guests - and myself - as comfortable and happy as possible. IMO, a gracious host allows his or her guests to make the choice of what would make them most comfortable and maximize their enjoyment.
Moreover, the inviter may not know the up-to-date specifics of a guest’s social/romantic situation. Again, imagine the possibilities. 2 years ago you went to college with a guy. You were really good buddies and you want him at your wedding, but you haven’t kept in touch as regularly since you got out of college. You don’t realize that he has been in a torrid relationship over the past month with someone he considers may be his future lifemate. What a potentially uncomfortable situation you would be putting him in, having to expllain to his new sweetheart why he really wants to go to your wedding, but why she is not invited.
If finances are such an issue, then I suggest the preferable option is to scale down the invites. Or, cut down other expenses to permit you to invite more bodies. Or have a very small formal wedding/reception, and then a big low-budget party for everyone and their guests.
Speaking personally, I always wanted to attend weddings stag, as they were among the best opportunities to get laid. Hell, in high school and college, my buddy and I used to put on suits and head out to the hotels around the airport and crash weddings. A smorgasboard of open bars, live bands bands and DJs with no cover charge, and plenty of single women in party mode.