I am now the proud owner of 3 MTGO accounts and am working my way through the free New Player Points that come with each account and allow you to enter special new player events. At least they're called new player events, so far my opponents are divided about 50/50 between people who are genuinely new and veteran players brutally farming them.
One opened account costs $12 (in the UK) and gives 5 free tix (equivalent to a dollar each) plus the chance to win 2 tickets from the 4 New to Magic Online Phantom Sealed events your points let you enter. If you get 2 or 3 wins (which roughly corresponds to the top half) you get a pack with a load of very common cards and 2 tix. So potentially you spend $12 and get $13 back if you can place every time.
Another way to look at it is the cost to enter limited events. Magic limited events (where they give you a small set of random cards as part of the entrance) are a ton of fun and even the playing field against veteran players with huge card collections and all the strongest cards in their decks. Most Magic players like Limited and are quite prepared to lose value just for the fun of the events. From that perspective $12 buys you 4 Sealed events. It can be a great way to look at the new cards when the next expansion comes out.
Magic experts have calculated expected value (EV) of participation in events in great detail, there's even a calculator available. Looking at that you can expect a loss of 1.99 tix every event, or in other words if you count cards as equivalent to money it costs you $2 per event if you have 50% win rate. Except those are averaged expectations, the prizes are skewed towards the most successful. On average it costs $1.99 but that counts the guy who usually wins 4-0 and walks off with 11 boosters whenever he does. An average player, never getting 4-0 but also never getting 0-4, with an even amount of 3-1, 2-2 and 1-3 results will get 6, 3 and 0 boosters for those results respectively, which is 3 on average. The event costs 6 boosters and 2 tix so about an $11 loss per event. Or $11 for 3 hours of fun if you prefer to view it like that.
$12 for 12 hours of fun seems a much better deal, or including the prizes and free tix with a new account, about $1 for 12 hours of fun for an average player (I'm assuming playing in the newbie events is worth a free win every time so you'll get 2 wins 3 out of 4 times for 3 wins of 2 tix each, plus the free 5 which is 11 tix per account opened. In other countries sales tax is less so you pay closer to $10.
Now is it an error to equate game value to value in actual money?
Well according to this article investors have used out of print cards as a method of achieving a return on investment that outperforms the leading mutual funds. People take these cards astonishingly seriously.