If you aren’t getting married, why do you feel the need to have a party? What would this celebration be for? What would the ring be for? Would it just be a gift, or would it “mean” something? Do you plan to stay together forever, or not? Is this just a ploy to receive “wedding” gifts? (Pardon me for being so blunt, but if I were invited to something like this, that question would cross my mind, and I am sure that I am not alone.)
My opinion is that, since you noted a lack of money, you should either a)forgo the whole thing or, b) wait until you have bought and moved into your new house and then throw some sort of housewarming party. Perhaps a barbecue or a potluck. That way, you can show off your new house, and most people will be able to infer that you two have, indeed, shacked up. It will be quite unlike a wedding because it won’t be a wedding at all, or even a psuedowedding. If you want to hire a DJ and have a dance, or have a cake, or play charades, or whatever–go ahead, do what you can afford. If people wish to bring you housewarming gifts, that will be their prerogative. Any other commitment that you two make should be made in private. There should be no public “ceremony”.
You see, I would feel a bit odd about attending a “commitment ceremony” for a heterosexual couple. If you wish to commit yourselves to each other, then you can do that privately (and for free). If you want to proclaim that relationship to your families, friends, and the community at large–well, that’s what marriage is for. I, as a witness, would not really be sure what some other kind of ceremony was signifying, and why I needed to be involved if it’s not a “real” marriage. Do you know what I mean? I’m not sure why you and your girlfriend are “firmly opposed” to marriage, but it seems to me that you would like to reap at least some of the benefits of marriage. So, why are you so opposed to it? Don’t be surprised if the world at large occasionally refuses to recognize your relationship without that “little piece of paper,” especially since there are fewer and fewer states which recognize “common-law” marriage. If you happen to live in a state that does recognize common-law marriage, then this little ceremony (and the ring) would just add to the outward evidence that you are indeed married, license or not!
You certainly have the right not to get married. You may have a very good reason not to. But, IMO, if you are going to throw a wedding, have a ceremony, and exchange rings in public, you should be getting married. Anything else seems like a sham.