Hello Jonathan,
My 2 cents, just as the guys said above itās not going to be cheap. But you can start by combing through all the recent built threads on this forum first, this will certainly take you some time, but after that you will be fairly familiar with all the tricks and the get-arounds for building a TK costume.
Use this extra time to save up, and check out our buy and sell section on a regular basis, you might be able to find a pre-owned but not yet build kit for a little less than what it cost originally (sometimes people just let them go due to lack of time to start a project or other issues). Planing and actually building a costume till itās ready to troop will takes months (if not years, from somome I know from my garrison).
Just a warm reminder on joining the Legion, it's not just about getting into a costume and look cool, itās also about your love for Star Wars and to share this love with others, and while doing so, give a little back to the community (you have to be prepared to give up some time for charities and stuffs).
Good luck.