Edition 30 and Pirelli cars demand a premium, but personally i think they are overpriced.
As a useable everyday gti a stage 1 remap and maybe a good intake filter, precat removal, this will not break the bank, anything after this will start to get expensive
Concentrate on service history, a 100k car with good history is fine.
try and get an 06 and later with the BWA engine code, as these seem to give less trouble
i would say 4k will get you a perfectly good car, with no issues, or buy a cheaper one, and expect to spend money on it.
Mine was an 100k 06 5 door DSG with decent history including gearbox services, but i wanted peace of mind, so changed timing belt, thermostat, intake clean, oil pick up and sump clean, pcv valve, cam follower, diverter valve, oil and filter change, along with a Revo remap, used EVOMS intake and resonator delete, this added £1300 to the purchase price, but it is now a good quick practical car, which makes all the right noises!
I am sure many other will give their opinion, but plenty about and with the current COVID 19 situation, you may be able to pick up a bargain.