Decide if your sustainable target audience (those that come back after the competition) are even interested in contests. I agree with Johnn - you will probably find short term wins quickly dissipate as soon as the "prize" drops off.
Some market sectors drool over contests and some do not. Ends up being the same old people who reply and the pool gets smaller over time.
Leverage creativity by providing "subsidies" and matching people with great ideas with people who are great technical resources.
Offer 80 x $250 "scholarships" or "sponsorships" for teams/groups who put up the best plan to not only use the money, but pay it back plus a small percentage and create an ongoing pool of liquid funds to share around. Nothing new in micro-finance ideas, however if you slice your niche and look at how many opportunities there are for people in the domain/programming/webmaster world multiplied by the % who struggle to implement, you could probably have an ongoing following of loyal micro-loan developers and imagineers who when put together create 1 in 100 blow-away themes/sites/ideas relating to your niche.
Sustainable advertising and marketing is directly proportional to the length of success. Whether it be word and mouth or multi-million dollar corporations. The bigger the wheel, the more fuel it takes to turn it.
Look thru the eyes of your audience. If I'm a webmaster - what am I really interested in? Lower costs - faster services - quality hardware - responsive contractors - latest themes and technology - reliable peer support and advice - less spam - less scams - more customers??
If I'm a webmaster what would attract me to your site??? The ability to find either all or some of the above in a way that is better than I can currently get.
Sometimes that is simply about more visibility - but when the dust settles and you have to compete on the same turf as everyone else - how are you going to differentiate your service - your pride and joy - your 20k investment that is now gone - from everyone else???
By having a sustainable and continued approach to whatever you are doing and doing it to the best of your ability. There is no substitute - outsource the expertise if you have to.
If the 20k prize will bring you 20k plus a dollar or more in revenue, and you feel it is still worth the effort - no problem - go for it. Offer something more than money - something that your audience does not have or can not readily find elsewhere. Do a deal with a hosting company and double your 20k to an effective 40k worth of prizes and offer "discounted dedicated servers for 12 months"
There are probably a thousand ways to create contests and leverage your cash position to get a greater return. All I am saying is make sure the long term bang remains after your buck is spent.
Good luck!
