I agree - I think the cost of quarantine adds up pretty quickly. You may want to look into that before you decide to skip the process entirely.
The only "cost saver" would be in possibly being able to ship your pup as excess baggage in the plane rather than cargo, but you'd need to check into whether the airlines would do that. I think, if I remember correctly when I was looking, a lot of airlines specifically say that for the UK they only do PETS-compliant shipping (so that wouldn't save you any money anyway).
I do remember someone posting about having their dog(s) stay in quarantine in France rather than the UK, because it was cheaper there.
ETA: Regular dog kennels (in London) are £15+/day for a dog. I can't imagine that quarantine would be cheaper (as there's the quarantine part to be careful of, in addition to regular dog care), but even if you assume £10/day, that's £1,830. Plus VAT (so £2,187). Unless your border collie is massive or you're flying from the north pole, there's pretty much no way airfare will cost that much with the PETS program. (And the vet visits are pretty cheap in comparison as well.)
Personally, my dog would do "fine" in quarantine (he loves people), but he would definitely wonder WTF just happened to his life. He would miss going outside and being petted by everyone, and I wouldn't have subjected him to it. YMMV, though.