Windows Web Server: $400 SQL Server Express: Free (Databases have a 4 GB maximum size)
I can't image how it would cost them 5 figures to use asp.net mvc. I find the productivity of the MS development stack to be well worth the meager cost.
Take stackoverflow.com - a hugely successful site that I believe runs off 3 servers (originally 1). Jeff and Joel put this together on a pretty tight budget and I bet their site handles a bigger workload than the OP's site.