I like free, send me one to check out as well
As for what to include and what not to include...
How about this,
Any ore/enmatter/treasure you have globaled on while running your client software in the last 7 days is free.
10 user selected resources added for x.xx price
25 user selected resources added for x.xx price
all resources added for x.xx price
This would give people a taste for what the service offers as well as encouraging them to run your client more, but since most miners/traders don't global on everything they receive in a given week, they will still want to purchase your 'premium' options.