I'd be asking other companies (at least another 2) to evaluate what you need and give their quotes.
If they are all saying that you need the same level of gear then that's probably what you do need.
Remember that whatever you go with should have some extra capacity - for when you get that big contract and take on another 5 CAD users.
PS. Don't forget to ask for a raise when you end up administrating the new system, as no doubt you will.
It starts by them asking for advice, then ask you to look after the backups, then ......., and the job creeps up on you. (Been there, done that).