It is not allowed within the rules of "no external heating equipment allowed".
I have this one: Battery Warming Safety Bag-Muchmore Racing. Co., Ltd. But hardly use it.
With racing also not allowed but easy to fool people if you can hide the wire.

ROAR changed their rules, many years ago, to allow heating. Their temperature has been 90* or less, similar to TOUR.

There is also a plethora of knowledge of heating vs discharging and what they do and take away from the battery. I don't check this forum all that often, but you can message me.

how fast do you want to charge your batteries?? high end chargers can charge and discharger a lot faster like 40+ amps/ which is only a few mins of charging for most batteries. That also have nice screens with lots of nerd info that i enjoy seeing. But i'll tell you this, here in California the most popular racing for 1/10 scale is stock 17.5/21.5 racing and the vast majority the fast guys all have ichargers and all charge and discharge at 40+amps.

Going back to the OP's question...there are lots of good chargers that are sub $100 but most are DC based. You might want to invest in a 12v power supply that can be reused if you ever decide to invest in a different or bigger charger.