There is no reason the first frame can't be rideable, especially if you are willing to start with material that will allow you to work it post braze. It would by no means be a world beater, but it can be perfectly serviceable.
The Ceeway kit Wilfonzo is pointing you at is a good value IMO, couple that with a handfull of Peter's cheap stamped practice lugs and some tube to use them with and the worlds your oyster.
I'm of the opinion that a jig shouldn't be the second thing you spend money on. Most of your brazing will be done in space so the jigs main purpose is ensuring the puzzle pieces all fit together properly in the dry and while nice it certainly isn't necessary. Pins and Gravity can get you there as well.