Don't opt for a scooter to save money on fuel. In fact, don't opt for a scoter to save money on anything, period.
My Vespa PX200E EFL for instance uses 5.3 litres per 100km on mixed riding, unloaded (eventhough the brochure says something like 2.2 or 3 or something). Loaded, it uses an average of 5.5 litres on decent roads, and 8.5 on horrific roads (mud/sand/washboards. If I remember correctly, a BMW GS650F Dakar uses about 3.5 Litres (somebody corret me if I am wrong). The Vespa PX200E EFL is a two stroke of really old design, and newer four stroke scooters would offer better mileage. Still, the underpowered engine and the heavy loads you would be hauling, would translate into high revving and increased fuel consumption. Small engines have to work hard to move you along fast, move you up hill, move you in head wind, move your heavy loads, etc., using lots more fuel than a bigger bike doing the same job.
Other issues, take for instance tyre wear. A scooter's small tyres will wear a lot faster than that of motorcycle equivalent.
Small scooters are simply not designed to haul heavy loads, travel fast for long durations and distances at a time, or travel under harsh riding conditions in general... meaning that you are more prone to having things go bad, maybe really bad.
If you want to take the pragmatic and financial sound route, then trading in your scooter for a small motorcycle is the way to go. For the same price of your used scooter, you could likely get a decent 250-350 used offroader.
You choose a scooter for the same reason you would choose a chopper, Tuk-Tuk, moped, trike, or any other silly ride, because you just feel like it.
My wife and I will during June/July be riding two Vespas from Cape Town, South-Africa, to Kenya, Nairobi, a distance of about 6.000km. With everything that can likely go wrong, I will be carrying allmost half a scoot in spare parts. For the cost of all my scooter, my upgrades and modifications, spares, tools, etc., I could just about have purchased a stock BMW Dakar which would need very few mods, spares and tools. Well, this might be an excaggeration, but only a slight one.
However, if you have the time to wait for parts to be sourced and couriered to you in some desolate corner of the world, then you won't need to fork out lots of money for parts you will likely never use. But if you plan to go fast like me, then you need to be prepared for anything that have any significant probability of going wrong, and with a Vespa, that inludes just about everything you can think of, as well as just about everything you cannot think of.
If you have some special kinky and perverse relationship to classic rides or scooters, like I do, then go for it, if not, then reconscider.