nilch is quite an expensive project to maintain, especially given the current amount of traffic it's recieving. I sadly cannot offer you many fancy benefits for donating, however you can get a mention on the website with one of the higher membership tiers or early beta features with some membership tiers.
To give you a loose idea of costs, every thousand searches cost about AU$7.50. This may sound decent, but nilch has been recieving sometimes thousands of searches an hour lately which has been a massive shock which is difficult to maintain. Additionally, there are general server costs.
Donate!