Yeah, it's not a cheap game to get into. The smaller ships are around £10 each and the new capital ships go
up to around £65! The mat is from a company called
Gale Force 9. Lots of online shops in the UK stock them. Fantasy Flight are bringing out their own tiles to play on soon too.
I think you can have a decent game with just the starter box. Normal games are around 100 points a side, which will get you between three and eight ships. Imperial forces tend to have more ships as TIE Fighters are dirt cheap.