"Rhetorical" question: Any idea how much it would cost for a good IT expert to convert a peer-to-peer network connected to a server into a true domain set up? (server 2008, 20 workstations).
It's not a good idea to go with Server 2008R2 when it's the same price as SBS. Except with SBS you get a lot more for your money, Exchange, SharePoint, WSUS, and all of that pre-installed. An IT guy that could actually set these up properly would charge you a small fortune. Hence, I'll recommend SBS. Depends if you want SBS Essentials or Standard.
20 Workstations is a lot and if you think you will expand over 25 users/computers, you will need Standard.
Active Directory: SBS Essentials $400+Server Cost (1k-5k, depending on where you buy it)+25 Users (max) Free
Active Directory, Exchange (email), SharePoint (collaboration portal), Full On-Site Solution: SBS Standard $700+Server Cost (1k-5k, depending on where you buy it) + CALs (5 Users/Computers Free + $50/Additional User/Computer) + Win 7 Pro (100/computer, IF you have any computers that are not pro or above) + Domain Name ($2-$15/year depending on domain suffix .org or .com)+$50 (SSL Certificate for Encryption)
Labor: $70-200/hour (depends on the guy and how well he knows his stuff, some like to charge a lot). A guy that knows his hardware will save you quite a bit and get you really fast stuff. A guy who doesn't will spend a lot on the hardware. Bear in mind, it's pretty hard to find one who's good at both.
Imo, SBS Essentials setup should not be more than $100/hour. It's just way too easy.
SBS Essentials is geared towards people with Win 7 "servers". It's relatively simple to set up. Standard is for people who are looking for a fully integrated solution.