Bases are rather easy to cast in resin as they only require a one sided mold.
For the ease of mixing i prefer to use silicone and resin that has a mixing ratio of 1:1. I started with the
Smooth-On starter kit. It comes with basic resin and silicon as well as release agent and some material (a DVD and stuff) to get you started. I don't know where to get it in the
UK but the smooth on website has a list of distributors. There must be some in the
UK in the list there.
http://www.smooth-on.com/ You still need something to make the frame for the mold out(Lego block work well) and if you also want to make two piece moulds some plastilin or similar stuff to create the first side.