I nearly got a border but two things put me off;
Firstly they are no longer really bred to work so, I see a lot about that I would consider too big or a poor shape and you you don't know if they will work if their parents haven't been worked.
Secondly, they are now a kennel club 'breed' so of course pedigree breeders are selling them and therefore want an arm and a leg for them.
I really do like them, but I ended up getting a Patterdale instead, and I am glad of my choice for the following reasons: Working strain of dog, isn't too big and catches rats like nobodys busniness, wide genepool, as they are bred on working merit and it makes little odds to the breeder if he puts a border x pat to a pat or one that clearly has a lot of JRT in it etc. This also means you get lots of interesting coulors etc (mine is almost all black, but had a littermate that was clearly a borderesque throwout, who was also loveley). Final reason was I couldn't find a border for less than £400 and my pat cost me £150. Pattedales aint everyones cup of tea, but I like mine and I'm glad I bought him.