I bought a #4 last summer at a local flea market for 20 bucks. It was in good shape and just needed some cleaning and setup. The first picture is the plane with the knob and tote taken off.
The second picture shows the patent date. the japanning was probably 95% or better.
This picture shows the sole market to flatten. I used sandpaper of a piece of granite. The sole had a dip in the middle and it took a while to get it out. I started with 180 and went up to 400. It was probably overkill, but once I got the low spot out it went quick.
The next is after the flattening.
I gave the body, frog,and everything a good cleaning and sanded what needed it. I then turned to the blade. It had several chips and wasn't flat. I ground it back and put a 25 degree bevel and lapped the back to a mirror finish.
Here's a couple shots after putting it back together. I gave it a test run on a piece of maple and walnut. Not bad for 20 bucks and probably 2 hours time. I actually like doing this nearly as much as butchering wood.