My favorite cheap enclosure method is the one shared in this thread:
Also, where did you find a deal on 10 pairs of XT30, XT60 and XT90 all for 8$? I want that! 
+1 for Brian’s list for the order in which you should pick your parts
+1 for buying a used battery rather than building your own, it definitely is cheaper, unless you can find someone to lend you a spot welder and you don’t value your time at all lol
+1 for using a loop key instead of an antispark to save money
And I think a good single drive setup is the best performance per dollar option. Means 1 less ESC, 1 less motor, 1 less drivetrain. Also you can save money by using a non-esk8 front truck.
Ambitious goal, I wish you luck!