Welcome to the hobby mate!
Well, the first thing you need to know is that: You cannot get a fully build sub kit for less than a hundred dollars!

Imean, with the radio equipment and all.
Maybe these things could be useful:
-3 or 4 channel radio
-Motors, Servos
-paint, supllies.
-glues
-well, all the necessary you need to build an RC craft.
I don't like to discuss about prices so they can vary depending on what you buy, but remember: K.I.S.S : Keep It Simple Stupid!