I bought a bike for $20; thinking about doing a simple conversion to the existing wheels, with a single speed kit. Just something to ride to and from the store. Don't want to put a lot of $ into it.
However, I am wondering what size wheels would fit; it's got 26x2.125 on it now. Will a 700x28c fit? It looks like a mountain bike frame.

Is this correct?
700 C = 622mm
26" = 559mm

why not just shorten the chain and rock the stock wheelset?

700c wheels will fit on some/most 26" frames I think. Try it first before spending money on wheels though.

However, you won't be able to use rim brakes on such a bike.

Yeah, good call. I forgot to mention that.

I was just thinking of getting some cheap wheels, a little better than stock, super-cheapies.

I measured 700 wheels from another bike and they look like about 28" in diameter. Don't think they will fit on the fork I have, however, they may fit on the frame.

I may just stick with these, throw on some road tires...

The frame has chrome stays... maybe I can make it look like a baby Madison.