I use Nissens for the Audi heater core replacement kits. They seem to be a fairly big brand in aftermarket heater matrixes..
I did see £7.50 price tag and thought it had to be a mis-print... the Nissens units seem to be pretty solidly built from the Audi units I've had in.
Yes, Rave does have a pretty long process for getting the dash out, but it is the process to take the WHOLE dash out, metal framework and all. The version I use is just removing the top of the dash and leaving the metal framework intact. You then just need to remove 4 bolts to get the centre retaining bar out that's in front of the heater box, unbolt the heater box itself and remove one screw that holds the front half to the A/C back half and the whole box comes out.
The biggest advantage to doing the dash out, is that you can then obviously clean the heater box, and split it in half to give all the flaps a clean and lube (and shave if they have been binding up or hard to move).
Interested to hear about taking the steering column out though - take a few pictures when you do it to post up! Damn LHD vehicles getting it easy on that task!!
'06 4.2 Supercharged Black/Cream "Jess" -- Bought April 2021 (NZ)
'01 4.6 Vogue Black/Lightstone "Snog" -- Bought Jan 2012
'99 4.6 HSE Cobar Blue/Lightstone -- Sold March 2009
'95 4.6 HSE Epsom Green/Tan -- Traded June 2008