always wanted one, now that i am looking to replace my car, the prices are within reach

i see two problems. their rarity and the high mileage.
first of all, the rarity - the only places i have checked is ebay, the audi site, and pistonheads. there aren't too many results, and even less suitable ones. though, i will keep trying... where else can i check for second hand rs4's?
also, the fact i am in scotland probably means it will be ages away.
and then the mileage. due to the fact they are usually from 2006 era, most of them have a high mileage. you are probably doing well if you find one that has only done 60k! most are much more than that... 80k, 90k etc. how much of a problem is this? what is considered 'too high' a mileage? i imagine an engine rebuild would be catastrophic in financial terms.
i was looking to buy in december-ish.
thanks!