Sysadmin here. How much are you willing to pay? I'll need at least 2 domain servers, exchange server, backup server/device/nas/tapes, etc to give you a stable and recoverable environment. I'll need an air conditioned server room/closet as well and a decent UPS. We'll need to pay for offsite data storage as well. How many people? We'll need CALs for each user. Licensing even for a trivial environment is easily 5 figures. Not to mention my salary.
I guess you could go with some shitty MSP and small business server, but not if you actually value your company, uptimes, and data.
Cloud services aren't big because they're good. They're big because they're cheaper than guys like me and all the stuff we work with. Your boss understands this. He's expecting you to deal with it.