I still have 2 ramps my DH made when he was alive. They are the greatest, covered with carpet and very adaptable to moving around. I lso have a nice little set of doggy steps that are basically a covered plastic framework covered, but they work like a charm too. They are surprizingly sturdy. I think you can get them for $20. There is a product that changes from steps to a ramp on LTD commodities that looks nice and is very inexpensive:
Convertible Dog Stairs - LTD Commodities $16 - $18 depending on number of steps. I am thinking about ordering one to check it out.