Thanx for the reply.

Another question, are Mirage, Visions and Weatherlight cards readily avaliable through dealers and/or packs? To be more clear, Can I get any card ever printed on MTGO if I had the cash for it?
EDIT: Are fetchlands also legal?
EDIT2: And just how expensive are Invasion block cards?
What do you mean legal? Online play allows a variety of formats (Extended, Standard, Block) including some online-only events (altho PEs are not really going at the moment). These include 'Classic' (All online sets are legal), Tribal Standard, etc. Every card that has ever been printed online (invasion forward plus MiViLight) can be had for the right price, as there are lots out there and lots of bots and dealers around who will sell them to you. If you are willing to invest the cash, you can get that playset of Deeds or LED's or Fetchlands or whatever else. Packs of out of print sets can usually be found too, for a price like everything else, altho the longer the set has been out of print, the more expensive the packs as expected.
I *believe* visions and weatherlight packs can still be purchased from the official MTGO store, altho I am not sure on Mirage (I think they are OOP but not 100%).
Also, I just checked now and saw Orim's Chant for sale for 31 tickets (1 dollar ~ 1 Ticket), Vindicate for 31, Pernicious Deed for 41, Onslaught Fetchlands for around 10 each, Meddling Mage for 41. Those are most of the highest price cards (plus of course Tarmogoyf who is also around 30-40). Hopefully that will give you an idea of some of the prices. Otherwise, anything that is in print and isnt incredibly popular is usually really cheap, and even the most popular cards tend to drop pretty fast (Bitterblossom at 13 or so, compared to like $30 IRL).