Cheapest slip-on you're gonna get is either the Arrow Thunder or the SilMotos. Motovation has RG3s for $1K, Thunders are like $800 and change. That is unless you go used, but even then, they're still quite expensive for the "nice" exhausts. This ain't no Japanese bike with a Two-Brothers can.
Then again, I may be interested in selling my RG3s in the near future so I can get some slash-cuts.
I'm right there with you, man. There are smokin' deals on used exhausts out there, but you have to be fast when you see them. For the most part, they hold their value because of demand. I'll let you know first if I decide to get rid of my current RG3.