Hi,
Well here's an idea. You say you only have 300 daily visits, which for me seems normal, because even if you're interested in the product, you won't visit the site everyday to see if a new version has emerged.
Which makes me think that on the 2500 members, much more than the 300 might be interested to donate. So what you could do is send a mail to all your members and explain the situation. I'm sure you will have a lot more feedback and you could even evaluate the number of people willing to donate (and maybe make a poll on how much they would donate).
I think you have to take it into consideration in your business plan :).