Tiff,I used to scuba diving,many moons ago lol

get yourself over to Stoney Cove in Sapcote and speak to the guys in the shop,theyre a good bunch of guys and will see you ok.

They have second hand stuff in sometimes and you could pick up a set of fins for a good price.
Mask and snorkle I would buy new, but they will have probably 15-20 to choose from depending on your budget.