You need something of similar viscosity. Motor oil is alot thinner and is designed to be in a high velocity pressure fed bearing. Chain and bars cost more than the oil itself. IF you wanted to cheat on oil, you'd need something thicker, like used gear oil. Tractor hydraulic oil is thicker than motor oil, not sure if it's thick enough. I used to be responsible for oil testing reports for gas and steam turbines at power plants as well as checking out barge fuel delivery tests too. Motor oil is way different lubricant wise.
I use my saw infrequently these days. Don't cut for firewood anymore, besides bonfires at camp and trail cleaning. Reliability has it's price. Less time I mess with a broken saw, the more stuff I can do. Trips back to town for parts cost time. I get up at camp for 2 days of work or so and it costs me $110 bucks in gas. Brandon's race car doesn't like low test I guess.
I got a 15 yer old ms261, still going good with little to no repair work. Carb hasn't been touched. I use non-ethanol gas and stihl oils, stihl chains and bars too.
Regular Stihl oil is about 22-25 bucks a gallon. I've used the cheaper stuff before with no problems. Walmart's one is about $16 bucks.
Stihl's stuff isn't horribly overpriced. If I use good bar oil and avoid one chain breaking apart flying at me, I think it's worth it......
I ruined an oil pump in a saw by using drain oil from gear boxes at work. Don't know if it was the additives in the oil of if it ha some particulates in the oil. I stick to bar oil in the jug now. I buy the generic stuff from Menard's.