You could build yourself a decent minarelli engine with a pipe for $300.

Bottom End $65 https://www.californiamotorbikes.com/product-page/80cc-wildcat-bottom-end

Minarelli Kit $130 https://www.amazon.com/Singlac-70CC-Minarelli-Vertical-Conversion/dp/B0B93Y75VQ/ref=sr_1_1?crid=6Z1EIXM5G2FK&keywords=minarelli+vertical+cylinder+70cc&qid=1667222534&qu=eyJxc2MiOiIxLjUxIiwicXNhIjoiMS41MCIsInFzcCI6IjAuMDAifQ%3D%3D&sprefix=vertical+minarelli%2Caps%2C88&sr=8-1

Carburetor $25 https://www.amazon.com/Carburetor-Mikuni-Intake-Zongshen-Thumpstar/dp/B0887VG7FJ/ref=sr_1_16?crid=1KZ78VEJ2R8XN&keywords=vm22%2Bcarburetor&qid=1666992089&qu=eyJxc2MiOiI1LjMwIiwicXNhIjoiNC43OCIsInFzcCI6IjQuNDMifQ%3D%3D&sprefix=vm22%2Bcarburetor%2Caps%2C76&sr=8-16&th=1

Pipe (Welding required) $75 https://www.amazon.com/SCOOTER-PERFORMANCE-MUFFLER-EXHAUST-1PE40QMB/dp/B00MNTQGA4/ref=pd_lpo_2?pd_rd_w=rOE0q&content-id=amzn1.sym.116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_p=116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_r=EEGKYR165MQQV8YB9X73&pd_rd_wg=nbhxK&pd_rd_r=61bea94f-d258-49a2-8fc0-8b7f0ca4e0e1&pd_rd_i=B00MNTQGA4&psc=1