Sounds like courier work, which I'm doing right now, GMC 2500 cargo van. Courier work should always be per stop pay basis, or a percentage of freight, plus FSC. Right now I'm doing a combination of the two, half day is doing a delivery route, flat $15 per stop, rest is X percent of freight, plus various surcharges. A lot of the stuff I could do with my Prius (don't make fun) like envelopes, etc, but a few times a day I get skids, and the customer pays dearly for that.
Was doing a delivery route for a major nationwide office supply company, depending on how much/how heavy usually about $130 to $160 a day, about 100 miles per day. Because of the traffic type and being loaded to max GVW normally, fuel economy down to 13mpg. Current courier job lighter weights and more open road, fuel econ more like 16mpg. The higher fuel economy of your van should help, but I would not do a fixed pay per day route. Piecee/per stop/miles traveled only.