Don't your servers already have BMCs supporting IPMI to provide full remote management? Often features like full KVM will require extra licensing, but remote power on is one of the most basic features and I've never encountered a BMC that didn't provide at least that much remote control.
It likely depends on the mfgr. Supermicro calls it SFT-OOB-LIC. HP has standard and advanced iLO. Haven't tried the IPMI interface on Supermicro without a license, but basic power operation might work.
