Hi Reindeluz,
how long is a peice of string?!
There's cars out there that'll be £1000 but will cost you double or triple that to insure, and at the other end of the scale, £1300-1600 cars that'll cost you perhaps £800-1000 to insure maybe less!
have a look at other posts about insurance, and it basically comes down to a multitude of factors - postcode, type of car, garaged or not, alarmed and tracker or not, age of drivers, length of UK license held, any no claims bonus (you might get some transferred from the US) value of car etc etc.
As there's so many cars out there, you've got to start by looking at the style of car you 'need' - not 'want' ! look at aspects of maintenance and running costs etc and make a shortlist of perhaps 4-5 cars, then get insurance quotes for them. If they're all more than you'd like to spend, then you'll need to re-assess the cars again.
On top of that, the used car market and prices are all over the place at the moment, but you'll still see many examples within the price range you want.
Cheers, DtM! West London & Slough UK!