I was looking at donating via paypal for SR:O and discovered they have 2 subscription models.
Model 1 (a.k.a. Campaign Model):
Up Front Cost: $30
Additional Costs: Expansion packs
Notes: Once you initially buy the game you can play without incurring any additional costs. Once they come out with expansion packs (new cities, runs/missions, etc.) you'll have to purchase those packs to play that content.
Model 2 (a.k.a. Free to Play Model):
Up Front Cost: $0
Additional Costs: Micro-transactions/Premium Subscription
Notes: Create an account for free and play. The difference here is that if you want to buy in game items it'll cost you real money. I haven't found any further details as to if it is all items (which would be ridiculous) or just the better items. They also haven't detailed the costs. I assume that the expansion packs for the first model will also be available in this model, but I haven't found whether they will cost anything. Premium subscriptions are available so you gain money, reputation, and karma faster.
I play Planetside 2, which is also free to play with micro transactions. The costs are generally from $2.50 to $7.00 for guns/equipment. To buy them you convert you money to "station cash" to be used in game. Every now and then station cash goes on sale for 2 to 1 or rarely 3 to 1 so potentially that $2.50 gun costs $0.83 and that $7.00 gun costs $2.33. Anyway, I'm curious as to how SR:O micro transactions are going to run. They could add a cost to everything, but make things as little as $0.50 (or even less), or they could have most things available for in game money and certain "premium" guns/equipment cost real money. Who knows, but I think they're going in the right direction by having 2 models to cater to what gamers are looking for. They can make plenty of money off of the free-to-play micro-transaction server and still over other gamers the pure play style of the campaign server.
My question to you all: which version do you plan to play?