A forum with over 300,000 members should be able to sustain itself through sponsorship / advertising. One forum I work with has just over 150 active members, and through google ads alone they cover their server / hosting costs. The members of the site took it upon themselves to donate various items that were then auctioned off, and a member used one of those shopping merchandising sites to create mugs / pens / t-shirts where costs of them go back to the company and you make a small profit from them - no capital costs involved.
Emailing members asking for money is totally the wrong way to go about it,

and I would have thought a site such as DaniWeb would have known better, there are more productive ways of covering costs. Special areas for paid members, some sort of subscription - or maybe putting software and tech tips onto a CD and selling it - easy well thought out examples that will be productive and help raise money and will also benefit the members of the site.
Part of me would also wish to question the authenticity of the email from the site? I find it hard to believe that the particular site in question would do that? Still, could be wrong!