I'm not a climber, but I know the area a little. I know some people like to climb Lumpy Ridge, but don't think it is actually in the park. Point is, you don't need to stay in the Park. Like Kathi said look to Granby/Grand Lake. Or look south of Estes.

As far as climbing goes, are you going to climb Longs or are you a rock climber? Either way, opportinuties for climbing are wide spread and not limited to RMNP. The Taylor River Canyon near Gunnison has some great climbing and camping will be a lot cheaper. If you are looking to climb 14ers you might head to Buena Vista and climb the collegiates.

In general when looking at a map of Colorado lands, BLM land will have the cheapest, often free and unimproved, camping, US Forest Service land is next in expense, but will vary, National Parks are the most expensive. And if you use Reserve America, you often pay double due to a reservation fee.

Good luck,
sarah