I'll give my two cents. I think that most bunnies, but not all, will do better with a partner. But, you really should let your bunny pick out its mate. Nothing is 100%, but if you let your bunny find the one that it wants to be with, and one that wants to be with your bunny, you have a much better chance of a bonding. If you go pick out a bun and bring it home, there is a chance that they just won't get along. I have see a couple of threads about people doing bunny dates.
When I got Bert, I knew that I would end up with two. I really probably should just have gotten a bonded pair. I don't really understand the whole bunny bonding process. When I got number 2, I just gave Bert back to the rescue I got him from and said I wanted another. For the first days they had him, it was mostly bad news. Girl after girl wanted nothing to do with him. They actually said that they may not have one for me, that is how bad it got. But, they did find one.
As far as the expenses go, the only real expense that is that much extra for a bonded pair is the vet bills. The extra amount of hay and greens, the extra amount of litter I use isn't really that much. Those are pretty small incremental costs.