As I mainly build ants, and lots of them, I would say a DSM2 transmitter is essential, as it allows you a source of very good, small, and cheap receivers. If you're planning on building more than one robot, then it will probably be cost effective to get yourself a dx6i. Or even as Dave suggested, get yourself a cheaper DSM2 transmitter. There were some blade ones on eBay for a tenner recently. Not packed with features, but they will do all the basics.