Yep, they can very often cost many hundreds more like in my case:sad: The transmitter is the main bulk of the buy which makes any size robot feel expensive, even antweights. You may not need a mixer though, all depends on if thats the way you prefer to drive. personally i dont like the things, but most people do.
Also, it may be worth your while if you speak to a few companies or send some e-mails round for some form of sponsorship as this will help you alot in the future. It means that any ideas you may have for improving your robot can have a hope in hell of ever being produced lol.

best of luck