Performance wise, there are great boards, good boards, OK boards and bad boards. It will take some time to find out which boards you should be looking for. There are many good starboard boards, but not all. Research on this forum will help you identify what to stay away from. Then when you find a board, follow Gyurmo's advise, plus it will be helpful to get someone with some knowledge to help you look at the board.
In the US, there are good used boards between $600 and $800 (without a custom fin).
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.