I'm not greatly familiar with the UK market but in the US I think $38K could get you a nice four aileron certified single seat S-1S Pitts with 180 HP and CS prop, and $20K could get you a homebuilt S-1C with 150 HP and FP prop. A close friend bought and sold a C, then bought an S last year at those prices.
What they were selling for 15 years ago is what they're selling for today, with no adjustment for inflation. I think they are a bargain for the right buyer.