Originally Posted by Hondo6

Assuming it's in good repair, the RD-M200 should work nicely - particularly if you are sticking with a freewheel and not planning on using extreme gearing.

Shimano docs say the long cage version of the RD-M200 (GS cage) will handle a 12T smallest cog, a 30T largest cog, and has a total capacity of 36; the extra long cage version (SGS cage) will handle 12T smallest/32T largest and has total capacity of 38. (In practice, I don't think you'll have a problem with an 11T smallest cog if you can find a freewheel with one. Not sure how far you can "push the envelope" vice largest cog.)

The most common current 7-speed freewheels seem to be 14-28, which the RD-M200 should handle with no issue at all. Those can be obtained for a reasonable price.