The transmitter is something I feel you should never skimp out on. People spend hundreds if not thousands on the robot and then drive it a round with a poor quality transmitter & receiver. Do it properly and get a Spektrum. A 5E is fine but it will make using it on multiple robots a bit of a pain. 6i has issues with some ESC's like the Hacked TZ85A (There is a solution for that).

It depends what you want from the receiver; number of channels and types of input. Even if you went and bought a DX7 ( http://www.ebay.co.uk/itm/SPEKTRUM-D...-/360827706687 ) If you build 3 robots, the cost per robot drops to £46. And given you may own an Ant, 2 Beetles and possibly 2 Feathers in the long term its not a bad idea.

Note: That is the lowest O have seen a DX7 in a long time! £140 for that is very good!