Interesting question. How many users will you have?
there are many companies who offer enterprise level email. With the hosting service, you are missing few features vs Office365. Your own hosting email will definitely be cheaper.
Another cost effective option that works very well and is free for upto 10 users is Google for Business - great collaboration tool with calendar integration, google drive and spam filtering. When you reach over 10 users you start paying $5/user/month. Again great for upto 10 users. You will forward all your domain email to Google, and your Gmail will look like firstname.lastname@example.org