Replacement standard V6 engines are fairly easy to come by. You should have no trouble sourcing one and getting it swapped over for well under a grand. If you're swapping engines anyway though, I'd be tempted to go for either an ST200 (still 2.5 but with uprated guts and a bit more oomph) or ST220 (3.0 and significantly more powerful). The labour charge for the swap will be pretty much the same for all three, so it's just down to your choice of lump. I know they're a trek from you (I imagine you'd need to trailer your car there if your lump is already seized), but by far the best the place to get the work done is B&M Autos is Bolton. Affectionately known within the club as 'The Bolton Mafia', their work is of the highest quality, the proprietor (Nick) knows Cougars inside out, back to front and upside down and the labour rates are very reasonable too.