I think it's a great thing to have happen, prices are now @ $200-240 per oz in northern CA for MMJ card holders, this I've seen myself in hundreds of CraigsList ads for home delivery services mostly. Dispensaries may/would be higher due to overhead costs.
I don't think the price will drop below that number myself, that's the threshold for selling under the "not for profit" statutes and my feelings are that once legalized the price may even go up as 'profit' would be allowed on non medicinal weed, in fact imo it's going to be encouraged to bring the tax revenue up.