It's also dependent on the amount of capitol one has to work with. It takes a lot of money to run a lab, probably more than most people think. There are technicians and students to pay, equipment to buy, consumables such as pipets, gloves, glassware, chemicals, etc. Just recently we put in an order for almost $10K in just antibodies and reagents alone . It could take a considerable donation to fund a single lab doing any type of research and you wouldn't necessarily be guaranteed any progress.
If you can't manage that kind of scratch, you might consider a donation to some organization that works towards some specific goal, they could perhaps more effectively allocate your money towards furthering research efforts. St. Jude's Childrens Research Hospital for children with cancer and other diseases comes to mind, but there are many, many organizations out there that could use your money. If you have a specific area of research in mind search the web and find out some contact info. and then look into the organization thoroughly before committing.