Well the $50 was broken down this way.
$15 - for cutting blade, primer, sand paper, and the Rub-n-buff (these will need for no matter what you use as a base for the armor. you may have to add or sub out item depending what you armor is made out of.)
Each 2' x 2' sheet of expanded PVC was about $4.38 I bought 8 sheets (about $35). You only need 4.
Unless you have all the detail supplies, they will cost about $15 leaving you $5 to find base armor material. The devil is always in the details and so is a alot of the cost if you are just starting out.