Indoor pet ramps

I'm thinking about either building a ramp or buying one for Cooper to get on and off the couch now that he's had his knee surgery (the other back leg is also luxating, so another surgery may be in the future) and he will need to be more careful jumping up and down.

I found a stair thing at Drs Foster & Smith for about $100 after adding in tax and shipping but was wondering if anyone has any cheaper ideas. I tried a piece of plywood with a cheap carpet remnant for now and he's not so sure about it. Of course, my homemade ramp is a lovely addition to the room and goes with all my decor (not) so I'd hate to lose it. The cat, on the other hand, thinks it's the best scratching post ever.