I've trained at home, and I've trained at a gym with a trainer. I prefer the gym and the trainer, mostly for the social aspect, and because my trainer makes sure I do what's good for me instead of just the stuff I like the most, lol. But, I know what you mean, it isn't cheap!
I'd suggest that you start writing up workouts for yourself, planning ahead, and maybe run them by your trainer, if that's appropriate, or find online sources for workouts, and keep your same workout time and days if you can, or some kind of "appointment" with yourself would help. A support group online, like one of the chat threads on 3FC or on some website you like, could help keep you accountable and just give you a place to post when you get a
PR on your lifts...it always helps to have somebody who cares when something happens, good or bad! You might also keep a gym membership, even though you won't have a trainer, but as cinthia said, if you belong to a Y or 24 hr fitness or whatever...a lot of gym have memberships that are pretty cheap monthly, so you've at least got access to equipment, and if you go at the same time every day, you'll likely meet some other lifters and be able for form some friendships there, some accountability and encouragement, that could help keep the workouts fun. Good luck!