Not much information have been released about the actual costs of the OnLive game service.
OnLive will be available in a variety of different pricing packages and tiers, competitively priced to retail.
Monthly gaming subscriptions should be comparable to Xbox Live which costs $50US per year.
The MicroConsole, an optional piece of hardware if you wish to play on your TV, is expected to cost substantially less than the Nintendo Wii ($250US). Possibly around $50US.
Playing on the computer requires only a browser plug-in, a free download. See system requirements for more details.
Eric