I would suggest buying the best possible frame that applies to your commuter project that you can (equipped with everything that you may want: disc brake tabs, adjustable drop outs/fork ends, rack & fender mounts, etc).
That Proletariat frame is pretty gorgeous, though. Failing that may I suggest a Civia Hyland frame?
http://civiacycles.com/bikes/hyland/hyland_frame/
http://www.ebay.com/sch/i.html?_lnca...kw=civia&rt=nc
You can occasionally find these frames online (Ebay, etc.) for around $150.00 USD (plus $20 or so bucks for the drop-outs, $100. or so for the fork. It gets pricey pretty quick.). I suggest this one as it has sliding drop outs which make IGH applications super slick (no chain tensioner) and is pretty much commuter ready once assembled.