I'm going to stray off-topic and say that it's a very bad idea to go straight from living at home to living with a guy. Don't do it. You'll regret it.

If you two are really in love and if he really wants a future with you, he'll propose. In which case I'd still recommend you live on your own while planning the wedding.

Money-wise, you'll need to cover moving truck rental and gas fees, apartment deposit, application fees, and possibly first and last month's rent, depending on what your market is like. The only way to get a good estimate of this is to start calling around and checking prices.

Other than moving costs, I would save as much money as possible and put it into a "in case this doesn't work out" fund. Living together is hard, and frankly, you might not make it as a couple. If you can't leave whenever you want, you might end up staying in the relationship for financial reasons.

How much is that? Probably 3 times whatever rent would be to live somewhere else.

Well, I'd first decide how much I can pay in a month, then browse for apartment accordingly to both of your budget, find out the move-in fee, the deposit, the truck (in case you need to rent one to move your stuff)/move out cost. You also have to consider if things don't work out, that you probably have to have savings too so that you can either hang on for a few months (while looking for a new roomie), of course the best scenario will be that you can afford the place by yourself even if your bf moves out. Also consider the utilities bills, how to split things up, write an agreement on what you guys will pay in a month contributing to both rent and utilities. I'd too suggest that your job is pretty stable too in the middle of this economic time.

Signing a rental agreement is tricky too for the both of you since you both will be responsible for the place, if things don't work out, either one will be responsible for the condition of the place or if one of you broke the lease. Just watch out for your well-being so that neither of you have to end up in some small claims court later on to sue for deposit, etc (that's when the worst case scenario set it). Yep. It's a headache LOL.

I moved in with my fiance after he proposed, and yeah, I'm pretty lucky that the transition of moving in with him is pretty good since he's very laid-back and we get along well.

I would save up as much as you can. Moving expenses, deposits like mentioned above and then at least three months rent if possible. Make sure you have some sort of cushion in worst case scenario since a lease can be costly if you break it or you have live on your own. Good luck.

Oh, and don't forget that you might need some furnishings for the apartment..... that can cost you too. But one thing at a time!