Definitely Craig's list for strollers.  You can also try garage sales and kid's consignment sales.  For the ramp, here's an easy and inexpensive idea-- get a prefab shelf from you local Home Depot, then cover it with the grippy shelf liner; secure the shelf liner on the precut shelf with duct tape on the underside.  We did this and it worked like a charm and lasted forever.

We bought a telescoping ramp for our large moose, Tosca, because she was having trouble jumping into the back of our Expedition. We tried to get her to use it right out of the box, but she would have none of it. We finally laid it on the ground and had her step on and off of it, giving lots of praise and treats. Then put it on a slight incline and repeated the process, then a little higher. Now she uses it, no problem. As an interesting side-note, Rio (rear amp and all) did use it right out of the box… If there were cookies involved, she would do just about anything asked of her.

We also went the stroller route for Rio. I initially shopped Craig's list and some local second hand stores, looking for one of the bike carts for kids. Unfortunately, since we are fairly rural and stuff like that doesn't come up very often, the few I did find would have required a lot of modification to be usable for a dog (vs. human). They had small seats and such in them… We ended up going with a Doggy Ride stroller (which can be modified for bike use). It was a little spendy, but well worth having my exercise buddy back! My only complaint about it is that it doesn't have a hand brake. We live in a pretty hilly area, and going down a steep hill with a heavy pup-on-wheels with no brakes can be a little scary… Going back up those same hills, whew, let me tell you — you definitely get a work out!!!