yea, i spent a long time trying to make my own transmitter and receivers. they kind of worked for low data transmision rates.
eventually i just bit the bullet and bought one. they are quite cheap, simpler, smaller and *far* more reliable.
you need a transmitter and receiver on the same frequency. simplest if you stick to the same manufactorer for both.
for an example of a pair that will do the job go here: http://farnell.com
and search for this transmitter: fm-rtfq
and this receiver: fm-rrfq
(i don't think farnell's site works if i link straight to the product.)
there are a few different manufactorers making units like this.
they contain all the electronics for the transmitting and receiving. you just need to supply 5V and connect a small length of wire for on arial.
i used a tranceiver from these guys in my project: http://www.lprs.co.uk/main/products.php
(farnell.com supply these as well i think) because i wanted 2 way comunications. (i wanted the bot to be able to give feedback on batery level, temperature, etc.)
a tranceiver contains a transmitter *and* a receiver in the same module.
i can thourghly recoment those modules that i used if you also need 2 way comms but if you only want 1 way there are far cheeper companys providing similar.