Ask @liam about live API keys on the Slack forum. He'll probably give you one for free. Then when you register it, Betfair will ask about your betting intentions, turnover etc. So long as they see you as being a useful customer, there will be no fee.
I got mine about 4yrs ago before I knew you could get it free, but for lifetime useage, the ability to record the whole stream on all sports 247365, and the potential it contains, it's an absolute bargain. £2,999 would still be cheap.