I also run an adfree website, and subscriptions pay for roughly 50% of the 700 a month server bill.
Hearing feedback from my users, people are scared when they see recurring charges. I also charge $1.00 per month per user, but I do it at a yearly deal. 12 bucks per year. Their rewards are 20,000 pm's, the ability to delete their own threads in certain forums, and access to a subscriber forum.
Users know they are not really getting much for their 12 bucks, but hey, its 12 bucks and it is nice to see "customers" paying because they enjoy the forum. But if you get 1000 people subscribing, you can break even or make a couple bucks.
I gave subscribers a small icon under their avatar to signify that they were a subscriber. I think some people donate just to have that icon. You can see it here: (random thread)
http://www.greatlakes4x4.com/showthread.php?t=38075
I started my forum for the reason of ALL OTHER FORUMS dealing with offroad vehicles are so covered in ads, that they are just about unreadable. My "business plan" seems to be working perfect. I don't care if I lose a couple bucks a month, or make a couple bucks a month, its nice to be able to read a forum with .2 second page loads in an ad-free environment.
Now that we are in the days of unlimited mail boxes from google and yahoo, is it really necessary to offer up an email address? I can't think of any people I know who would pay for an email address.
I use paypal for all transactions, including my online store. Its easy to use, and since I do a once a year subscriber model, I only pay the transaction fee once per year.
Hope this helps