aviationservicescompany.com
$150 for the plane (wet) plus $44 for the instructor. He also offers prorated rates for the current multi pilot looking to build time. Pro rated rates are on his website under multi engine class rating.
I've searched everywhere and this guy is the cheapest I've EVER seen. Again he doesn't allow rental but it is still way cheaper than just renting the plane anywhere else. Well worth it. He had a pretty flexible schedule and a ton of experience too.