oOple.com Forums - Cheap small 2.4 receivers

Theres quite a few to choose from. Obviously the SMD as above.

Theres also DasMikro that sell some extremely small ones and also ones similar to the SMD/Sanwa style. I have one and it works great.

Another company is Corona (they existed before the you know what :) ) I also have the Corona R4SF and C4SF-HV, both work great and the R4SF is very cheap, used to be able to pick them up for about £11 a few years ago.

You can get them from Aliexpress or eBay.

Last on my list is the HPI RF-11, not easy to find these days but work great. Used to be able to buy one with a wheel transmitter for about £18 until stock dried up. Sometimes pop up, managed to snag one on eBay for £1 delivered a little while ago.