Hearing aids are smaller than that and look what they cost!!!! Replacement parts are not priced by their size. They are priced and made available on a demand basis. Outboard motors are not produced in very large quantities compared to cars for example. If you are mechanically handy you can rebuild the pump and perhaps it is just one seal that's leaking. Or, as pointed out, many just convert to pre-mix by installing a fuel-only pump. Big outboard motors (300 HP Merc for example) can easily cost more than a small car and it doesn't even come with a heater.
