You could build an entire WW2 sim out of freeware, especially with talents like John Young (remember Duxford?) at work.
He and Brian Clarke recently released a couple of WW2 UK bomber airfields on AVSIM, with appropriate AI.
I went scratching for a Liberator, found I didn't have one, and ended up forking out $50 on the old ALPHA (now Virtavia) one.
OK there is an FSX model in the download too.
The figures are masterpieces in their own right, there are AI Jeeps

and of course, AI B-24's (The other scenery is based on Marauder squadrons)

