Kilfrost RDF is pretty good, if not cheap. Aeroshell 07 works well too.
Aeroshell 07 can be bought from
Silmid and yes I may have got fleeced but hey this is aviation. £151.28+delivery so nearly £200 for the 20 litre drum.
The other small point is that unless you are built like Geoff Capes, the 20 litre drum is damn heavy, so one needs to decant the stuff into smaller more manageable containers. Of course these must not leak especially if carried in the plane! I carry a 2 litre prop TKS refill container of fluid #7, I bought a quantity of
these HDPE bottles which are also safe for carrying IPA (for putting into avgas, 0.5% to 1%, for high altitude flights at -30C or below - not that I know of a single case of TB20 fuel icing, unlike the Aztec in which it is reportedly endemic).
There is a lot of other de-icing stuff around, much cheaper, but one needs to be careful with "car" chemicals. I know of a TB owner in the USA who wiped out his £3000 (?) windscreen by applying Rain-X to it
All that said, if you have to pay £200 for 20 litres of #7 and have to spray it all over the plane after a cold frosty night with no sign of the temps going above zero, it's going to cost a packet.