that really depends on how good quality you want for your sails,plus the dimensions, i have a redwitch which is around 20ft, i recently purchased a carbon mainsail for 1700.00 by UK halesy-freo, but keep in mind this is top of the range racing sail, if you want a cruising sail, you're probably going to go for a dacron sail, where do you live?
i know in perth there are heaps of sailmakers who can do any sort of sail you want, and more often than not there are smaller chains who can do cheaper sails, sacrificing effective sail shape and overall quality. Geoff Bishop at UK Halesy was more than helpfull, they offered a lot of options and advised me on the choice of sail, the top of the range people like UK halesy will ask you what sailing qualities you want from your sail and will also take into account weather helm and other steering tricks with your boat,
i hope that helps

good luck