There are some threads about this deep in the pets board. Take a look there (or take a shot with the search function)
Alternatively here's what you'll need to do to find out your specific costs:
1) call your Local USDA and see what they charge to certify the paperwork and
2) call your vet to see what they charge you for filling out the forms.
3) Look at defra's website to see approved routes from your area and call those airlines about their costs. Ask about kennel sizes and then...
4) Look on various pet store websites for costs of the proper size kennel for your airline/kitty. Don't forget accessories like water bottles and absorbent padding, etc. all of which will be required by your airline.
** don't forget there are some cruise boats which are approved routes of travel with pets
The way around the 6 month wait is quarantine
Those are the 2 options. The PETS scheme is by far the cheaper option monetarily though costly in sanity loss.
Throughout the process you can call a DEFRA pets helpline who have been exceedingly helpful to me in the past (and others). I have heard tell that you can also fax them your paperwork in advance so they can give it a sanity check to see if you'll have any problems coming through.
Key things to remember:
1) follow the rules to the letter
2) do things in the proper order
3) don't leave it up to your vet, its your responsibility to check and verify all paperwork and the process. if the paperwork isn't done right you lose out not the vet
4) get originals of everything
5) make sure the microchip number is on everything
6) don't let any rabies vaccinations expire (this is key if you don't move before your kitty needs a booster vaccination)