Grand Coulee Dam

If you're coming from Spokane, is it fair to assume you're traveling via hwy2 and taking 174 north at Wilbur? This puts you off route for most of Banks Lake, where there is lots of free drycamping at WDFW-managed public access areas...

I've camped at Buffalo Lake on the Colville Indian Reservation- about fifteen miles northeast of the dam. Fifteen bucks a night, no amenities...they do have hookup sites but I don't know the rates.

Here's an article about Buffalo Lake.

ON EDIT

Found the current rates- twenty bucks now. Here's a link to the "resort" that I camped at- you'll note that it's cheaper to rent a CABIN than it is to rent a full-hookup Rv spot! I think the cabins have no inside plumbing... The whole place is a hoot- real throwback to the camps of my childhood.

Just south of Electric City on Osborne bay there's a cheap area. Farther away in Coulee City is a nice CG on the south end of Banks.

You might find the Dry Falls/Sun Lakes area too far away at 34 miles.

There is a nice state park at Dry Falls. That's not too far away. There is also a lot of what appears to be free dry camping along the lake south of the state park