it's going to run a lot more than $50 to do it right but probably less than $250 by the time you've bought the fiber board, jacks, gooseneck, paint, handles, speaker cover, wheels (optional but recommended), door latch, door hinges, mic, and speaker. i recommend a WEBER or Celestion speaker.
i wouldn't use anything less than 3/4" medium density fiber board for the box with 3/4" or 5/8" plywood for the speaker baffle.
definitely use a lot of screws and glue (a must).
it's not a piece-of-cake to make but also not that difficult if you have a table saw and the proper drill bits.
when i played clubs with it, i used a Sidewinder. i blew the first Sidewinder during a gig one night. now i have a Celestion Vintage G12.
-kp-