$44.00 per quart or gallon? 4 Quarts was it $176?
Can always offer to supply your own oil.
That engine will run fine with off the shelf 5W30, I typically recommend 10W30 for any LNG/propane <100kW power generation application in north america, less chance of sheering, generators have block heaters cold start isn't an issue.
Larger gas engines (over 13L) use Mobil1 Pegasus, which is SAE40 low ash/ low zinc.