I think the right scooter and a small custom made trailer might be your best bet. It might cost more in the short term, but in the long run it would be way better. 50CC is too small for normal speeds, but when I was a kid I had a three route paper route that I did with a 50cc Puch moped. Too many years ago to remember the number of papers, but it seems to me that it was not far from the number you have. The Puch moped had a step through frame and I stacked the papers in between my legs on the stepthrough part of the bike. On my Sunday route I had to make 2 trips, but I didn't have a trailer. People in 3rd world countries put crazy huge loads on mopeds, scooters and motorcycles. I have seen pics of whole familys of five or six on very small motorcycles and scooters. A 150cc or 250cc scooter could haul you and the papers most likely. Sunday might be a problem, but building a small trailer would probably solve that problem. A bigger scooter might hold the whole load of papers better than you think, but they would need to be flat and stacked. If you deliver folded papers it would be more dificult, but if you built your own trailer or modified a bicycle trailer you could probably haul all your papers even if they were folded. Another idea would be to make large saddle bags to carry the papers. Here is a link to an older style Honda that would probably do the trick. It's a 250 cc has a large trunk, a back seat, goes about 75MPH and gets about 75 MPG. If I was doing a route like yours it is the bike I would want to do it with.
2005 HONDA Helix (CN250) for sale in Avon, OH: SCOOTER - CycleTrader.com
Later,
Allan Greenblazer
Later,
Allan Greenblazer