Yeah, there's definitely better and easier to maintain transponders out there
. Trig make belters. We had a GTX 328 in a Warrior and the encoder failed, it cost the price of a new trig unit plus fitting (which was a crazy sum for 3 minutes work!) to replace.
Buying new factory built limits you as to what's available.
For that money, I can think of 3 planes that you can buy off the factory floor that are side by side and none of them really reach the speed you're after. There will be a few others but none that I'd want to buy
or perhaps that I'm aware of but they definitely cannot and will not be able to fly IFR.
RV7 recently built by a well known decent builder is in my opinion your best bet you can change the avionics relatively cheaply to whatever you want
. Fast economical, fun, plenty of loadspace, range and flexibility to do what you want without taking it from the CAA in charges.