I tried to sit down and find the cheapest parts needed to build your own Go Kart Mower. - all though I ended up ordering some extras. - Alloy wheels and the Hydraulic Brake Kit.
The Cheapest I could find were at BMI Karts & Supply.
Parts came out at 837 USD Engine and the Steel for the Frame NOT Included.
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https://www.youtube.com/watch?v=xOR1p78Z4mo