If you want a nice, but cheap onsen ryokan, Kyoto is not the place to look.

If you check out some prices in different areas of Japan, you'll see a higher class of inn for the same price (or less) in some regions:
http://www.japaneseguesthouses.com

From the site above, I found one cheaper onsen that looks like it has nice outdoor baths - about an hour from Kyoto. However, I've never been so I don't know if I'd recommend it.
http://www.japaneseguesthouses.com/d...haranosato.htm

My suggestion for people who don't want to spend so much is to stay at a regular hotel in Kyoto and experience an onsen ryokan in some part of rural Japan.