Well to actually answer the question...
Since you're starting with a Speedmaster, you just need to find a TBS wheel, then decide if you're okay with a 17" hoop. If not, then you have to decide if you want a stock TBA 18" hoop or want to go bigger. I went 18" and it cost me $220 ($20 for the hoop, $200 for the re-lacing). Add that to the cost of the used wheel and you're looking at about $600. YMMV. I believe someone just scored a TBS wheel recently for about $200 less than I paid.
Oh, and if you find a used TBS wheel, you'll probably want to replace the rotors and pads, just to be safe. And maybe buy a new tire depending on size (see above). Other than that, you've already got the right caliper, fork leg and master cylinder. Go sick.
