It's a steal, but also a risk - albeit a small risk from what we have seen with Turnbull. He hasn't played a full season in the Scottish Premiership yet and it's not unheard of for a player to have an outstanding year when he's 19 or 20 and then disappear off the radar.
While I have no doubt Turnbull can perform at a high level, so far he's not had the chance to prove it. (Turning down a chance of EPL football also raises a legitimate question about confidence to play at that level). Fraser on the other hand has proven EPL ability and experience.
The money paid in England is ridiculous, however and the billions generated is mostly spent on players rather than improving the experience (and prices) for fans. If you divide any transfer fee paid by an English club by about 10, that is the realistic fee you can expect in Scotland.
If he does maintain his form and rate of improvement, he could easily be sold for 20 or 30 million to an English team in a few years time. That is why we need to get the add-ons built in to that transfer.