Depends on how 'North' you are situated or how far willing to travel.
A lot of pro-riders will have horses they are bringing on to sell.
Other things will be price range, age/level of the horse you are aiming for.
A genuine schoolmaster which is sound but older will come cheaper but give you a wealth of experience. A friend sold her PSG horse a couple of years ago for £5K as he was 17yo and had reached his competitive limit. New owner downgraded him and he's still happily competing and taking her up the grades.
A young horse will vary in price depending on 'potential' - £10K is not unusual for a 3yo.
If you are really wanting a good horse at a sensible price it may be worth going to someone with your requirements and upper price limit and ask them to source one for you. The stud I'm using for my mare will do that for you and don't charge silly money - they have excellent contacts in the UK and Holland.
If you are prepared to work with a youngster from scratch it is often worth looking for a quality 3yo direct from a stud. I've had all of mine from unbacked/just backed and prefer to do it that way. My next one is my homebred 3yo