Know any of your good mates that may be struggling financially? Even 500 bucks to a mate in need and if he/she has any decency they will be eternally grateful and you will gain the status of 'top bloke'.
Failing that, i have 4 characters for you: W427
Failing that, a Mustang
Failing that, put it in a bank and let it gain interest $$
Failing that, update yourself with all the new-fangled technology
Failing that, I'll happily accept $1,000
Edit: if you buy either of those cars, you'll need to use the remaining money to buy fuel to run the said mentioned cars