I've been thinking about this lately. Computers that run RTW and M2TW engines, and their mods are pretty stinking cheap now. I just picked up a used Thinkpad X200 for a client's medical clinic (some ancient thermal scanner device that needs XP and RS232, don't ask), I picked it up for $100 and then dropped a 60GB SSD drive into it. For testing purposes I slapped Roma Surrectum on this laptop and fought a couple battles from a save file I had.
Granted I couldn't go all out and put it on highest everything, but I had it mostly on med-high, and a couple thousand men on each side of the battle and it ran fine, even on an old integrated video chipset. I also picked up an old Dell Optiplex for $50 to function as an iTunes server in my house, and I dropped a Radeon 6570 into it and it's running RSII, Stainless Steel, 1648 and Empire+Darthmod with everything maxed. It will even run Shogun 2 on medium-high settings. My point is hardware is cheap.

Has anyone ever heard of large scale battles fought on these old engines? I'm kind of half tempted to scrape together some spare laptops for a mobile LAN party setup. Maybe I would initially start with 2 vs 2 rig, but I started wondering about some four on four action. I could see especially if money was limited to 3-6k, and you had 3-4 people per "team" this could have some potential for some serious team gaming, one guy holding the shield wall, another skirmishing and a third running cav. It would also be pretty epic to see some HUGE battles too, I just don't know if it would be playable with 10-20,000 men per side. I think it would be kind of cool to have four lightweight laptops stuffed into a backpack or duffle bag, instant LAN party on the go...