If it were my 1st mower ever, i'd get a pressurized system ( has a spin on oil filter) and if possible liquid cooled ( has radiator). This would mean used.
I bought a used Honda rider
(twin cylinder water cooled 13 hp 38 inch cut with bagging system)
For less than $800 to cut my 1+ acre with 2 steep slopes. Quiet, well built, more REAL power than many 17 or 18 horse engines.
You can find deals everywhere if you look. Then after a couple years of used use, you'll really know what you need and can sell the used unit for close to what you paid for it.