I wouldn't decide ahead of time, see what's out there used. Sometimes other people's used is still relatively new, and also some old sofas were really made well. We live in NC, and there are some good antique/consignment shops in our area. Our old couch (solid sleeper sofa) was still comfortable but the fabric was really embarrasingly stained despite all my attempts at cleaning (would have needed to be re-covered) so we sold it. And then re-organized room so we needed a sofa that needed pretty specific dimensions. We looked over the course of a couple months, consignment, antique, craigslist and also new before making a decision. A couch is usually not critical so you can take your time with search. If you do buy new, learn some of the terms about construction so you are comparing like with like, price-wise.
Oh when we had our sleeper sofa it was 800 (a deal, nice solid Workbench piece with higher end queen mattress that saw a lot of use and was still comfortable), next a leather sofa with ottoman for 1100, previous to that, resale sofas (less than 50).