Try a look at Bopup IM server and it's messengers. Offered with one-time payment with no monthly/users fees and other "per-use" charges. The server and 80 users cost less than $1,200 US.
A lifetime license for Bopup IM server and 75 messengers is only $1,120 including free upgrades within 1 year period. They offer encryption, message archiving, file transfer, branding support.
Bopup IM which is based on a stand-alone messaging server. Logs history, secure, has clients for PC and Android platform. Much easier to setup and configure than OpenFire and other Jabber servers.
Try a look at Bopup IM as mentioned above in another comment. It is based on a self-hosted communication server, AD support is provided, that's you need for! Support is free and only updates are paid annually (not mandatory).