The amounts seem to vary by how badly they need the seats. Last week, they were offering $650 plus hotel to overnight in PHL to deal with an oversell on the last PHL-SJU, and $350 plus hotel for my PHL-DFW, also last of the night (to take a 24 hr delay to the same flight the next day). I actually don't think I've seen an offer under $200 recently.
Last year I took a $400 VDB in BNA (w/out hotel, didn't need one) for an Express 50-seat CRJ on a midafternoon flight, going out the next morning. I don't know if there's a different scale by equipment type, but I suspect that it's much more driven by their need for your seat and how long it will take them to transport you more than anything else.
Incidentally, I would say that I'm surprised I'm not seeing more VDB scenarios than I am given how full most flights are. Of the past 8 weeks, flying every Sun eve/Mon AM and Thu/Fri PM, I've only seen 3 offers on my flights. Every seat appeared to be taken on each flight.