A lot of people are successfully using a Raspberry Pi as a Stratum 1 NTP server. Granted, this solution isn't enterprise grade, and can't handle a huge load (it can probably handle a couple of hundred clients), but for about $50-60 US dollars, its hard to beat.
Microsemi and Meinberg also make enterprise-grade stratum-1 NTP servers. But, those run $2-3000 all the way up to about $20K.
