I can only suggest you stay away from Tecumseh engines -- I have two that are both POS. Very poor quality compared to Briggs, Kohler, Honda engines. Oh, and with that gravel driveway -- keep lotsa shear pins on hand and have a wrench and socket handy whenever you blow snow. Don't ask me how I know...
I have a 1970 Ariens purchased new by my dad, and the 35 year old five horse ran just fine for the 8-9 snow storms we had last season, including one of 25". I retired it for a new B&S 7.5, but it still runs well.
I also have an Ariens ST824 with a Tecumseh. So based on my equally large sample batch of two, they're perfect......
Tecumseh had virtually 100% market share in snow engines for most of the last 30 years or more.
Today most of the snow blowers using Briggs & Stratton are owned by Briggs & Stratton. This means competitors like Ariens and Toro are unlikely to use them, ever.
You can usually buy a 1-4 yo old Ariens used for 60-75% of the new price. You'd save enough to repair or replace anything, although repairs are unlikely. These machines are not complex.
With your budget you're probably better off keeping what you have.
