From what I've heard.... 95% of the eBay budget stuff is useless and a waste of effort to install it.... I've seen TV tuenrs for £30, but pretty sure they'll be a waste of time.
Is this for a generic screen or for an Audi RNS-D / RNS-E / MMI screen?
All my research is based on the RNS-E, so adjust accordingly
Remember that in addition to the tuner, you'll need the AV input converter which is anything from £30-£100, plus the aerial (prefereably two and then get a diversity tuner) and any wiring looms for integration into the head unit, such as a Kufatec box for the controls, etc....
I have been reliably informed (by somebody who has installed a LOT of these) that Ampire offer the best combination of tuner and Audi RNS-E integration (incl steering integration)... the
Ampire DVBT52 is the "budget" (£200) model and replaces the old DVBT100 model, the one I'm after is the
DVBT200 (£300 just for the tuner) which also has two additional AV lines in (for iPod video, etc) and this is the one that
HazzyDayz fit
for £650 incl labour, the AV adapter, 2 x aerials and integrated wiring loom, £580 if you don't need the RNS-E and steering integration and are happy just to use the remote.... which isn't bad if you consider the DVBT200 is £300-odd, the AV adapter is normally around £90 and the aerials are about £30 each... so that's £450 + wiring kits before you've even started doing any work or vag-com'ing stuff!
If you don't need full Audi RNS-E integration and/or can't handle the hassle of trying to source one of those, I've seen various people singing the praises of the
Alpine TUE-T150DV and
Kenwood KTC-D500E (both have twin aerial diversity tuners), but I'm not sure about how well they'll integrate with the Audi hardware as I've only seen those recommended for genric headunits.... and I think you still need the AV adapters, aerials and any other wiring, so that's £250-ish for the unit, plus the accessories, so probably still around £400-odd for all the parts.