I will, once the finances get better.
I'm not worried about the cost of ammo, since I have a Dillon RL550B that can load me 1000 rounds of 9 mm ammo for the cost of 70 bucks (or $3.50 per box of 50). It's the cost of the gun itself that makes it more of a seller's market.
The cheapest I could get would be a second-hand STEN submachine gun, and even then, that's still a hefty amount of $$$. Nevermind trying to get a HK MP5...