The reason they don't recommend riverwash stone for use on driveways is becasue it doesn't compact, so you can't plow it. But I shovel my driveway, and in my experience even compacted gravel comes up, so I ignore this issue.
Greely Sand & Gravel sells 3/8"-5/8" riverwash stone for $36.80 per metric tonne. Their supplies calculator converts riverwash stone at 1.36 tonnes per cubic yard. And their rectangular calculator converts 12.5 ft x 42.5 ft x 2 in into 3.28 cubic yards.
Thus my driveway costs 1.36 x 3.28 = 4.46 tonnes ~ 4.5 * 36.80 + $120 delivery + tax = $305 by visa over the phone. Delivery can be scheduled same day and is scheduled in half day chunks, i.e. tuesday morning 7am-12:30pm. You have to be present for delivery even if you paid in advance over the phone.