You could built a BPS (BlackBerry - BlackBerry Professional Software
) and just designate it as a test server. It is cheaper than BES, but has a cap of 30 users. It also does not get updates as quickly as BES (BPS is still on 4.1.4, so you cannot demo HTML with it yet).
Other than that you would just set it up normal. Make few test accounts and you would be good to go.