1) Impossible to know if $2000 is too much without more information on the domain. If it is mortgages.com then buy buy buy, if it is xmdj3S.com then don't buy!. 2) Always haggle, people will start with the highest price they can hope to get. 3) To value the domain you would need to know does it get any traffic from a keyword search? If not then it is not so valuable. Who else might be interested in this domain? If it is realistically only you then again that makes the domain not so valuable. Did they register the .com because you registered the .co.uk? 4) If you want to go international I would suggest looking into getting the .net domain instead, it will be cheaper and should still be good for ranking.
.com is recognizable worldwide and there is no problem to rank for any country that you wish. Just do a little optimization and with proper keyword research, you can rank highly and compete with any local site.