Here's a... ahem... "thrifty" way to get started with macro photography.
Find 1 or 2 cheap MF primes in the 28mm to 55mm range. While a K-mount or even M42 mount would be nice, it doesn't make much difference since you'll be using the filter threads instead.
Then visit eBay and find a cheap Asian K-mount reversing ring that matches the filter size on your lens.
I found an old Zenit 35mm camera, with Helos 44-M-4 58mm and Pentacon 28mm lenses, for a total of $5 at a yard sale last summer. I spent about $6 on the reversing ring on eBay. It took me a while to get the hang of it, but I was able to shoot this handheld with the 44-M-4 :