If you look at motorhomes that are new to a few years old now, those will likely be the ones you can afford 4 or 5 years from now. NADA has prices for used motorhomes, so you can see prices for rigs that are now 4 or 5 years old so you can get a little bit of an idea of what you want to look at. Just be aware that prices for used RVs are very depressed right now and may be a little higher if and when the economy recovers in the future.
It does matter what manufacturer you pick even for a used coach that is out of warranty. With the high fuel prices last year and a bad economy now, numerous manufacturers have gone belly up. Although many RV components like refrigerators, furnaces, air conditioners, hot water heaters and chassis components like brakes, engine and transmission are non-specific to any one manufacturer, and you still can get parts even if the coach manufacturer is out of business, it's nice to have the option of taking your rig to an authorized dealer (or even back to the factory) to have a particularly troublesome problem solved.
Another good idea is to read the owners forums here on iRV2 for the brands of rigs you are considering. This will give you an idea of what kinds of problems owners of those brands are experiencing. Don't hesitate to ask questions about reliability, service, etc.
Also make sure you get the right rig for the type of traveling you want to do. Don't just buy a nice floor plan or pretty decor. Make sure the rig has enough cargo carrying capacity (CCC) to carry all your stuff for the kind of trips you'll be making. I can't stress CCC enough because many rigs on the road are overloaded. Make sure the motorhome has enough towing capacity if you plan to tow a car behind. Make sure the holding tanks are big enough etc., etc.
Best wishes in your search.