That is by far the cheapest and easiest option. Buying the parts from Ruger would cost about $175 plus shipping, and if you are buying a blued gripframe it is shipped in the white, so it would still have to be blued. Ruger will fit and blue the grip frame for $50 plus minimum $20 shipping. You can buy a new Bisley Vaquero for $400,(less if you really shop around) swap out the parts and sell the resulting parts gun as a "lightweight Vaquero" or "Super Vaquero" depending on which grip they ended up with, for at least $300. Heck, put them up on gunbroker.com and call them "Custom" Rugers, someone will bite.
What it boils down to is this; if you are confident you can safely disassemble and reassemble a Blackhawk, and can afford to front the cost of a second gun, each conversion can be done for about $100.