If I were in your position, I'd budget it this way:
Ruger New Vaquero, .45 Colt ~$500, depending on locale.
500 rounds of .45 Colt cowboy loads, $180 or so.
Reloading setup, from $60 up to $500+, depending on what you want and buy into (I'm happy with a $130 LEE Pro 1000 progressive myself, but I seem to be able to make it work.)
ABCs of Reloading or NRA Handbook, and other reloading manuals.
Case of primers, $20 or so.
2 jugs of IMR Trail Boss, ~$30.
1000 Oregon Trail 200gr RNFP, shipped from Cabela's, $60
Add gun leather and accessories as desired.
But that is just a suggestion. I reload for my 629 and have worked up accurate loads in .44 Magnum and Special from over-grown .38 wadcutter level all the way up to "WOW!! What just whacked me across the hand!?!"