SAP's decision in July to move all customers to a richer-featured but costlier software maintenance plan -- resulting in an outcry from some customers -- could have a lingering effect, Scavo said. "I think it's caused buyers in general to start paying more attention to maintenance fees."

There's no clear sign that many more companies will follow the lead of companies like Rimini Street, which provide third-party maintenance at lower rates than vendors.

But these companies are already making an impact, said technology purchasing consultant and Vinnie Mirchandani.

"The thing about third-party maintenance that people do not often realize is just its presence/threat forces a lot of discounting from the source vendor," he said via e-mail.

A number of large outsourcers also provide maintenance "on the quiet" for customers, according to Mirchandani.