Worked out a in kart radio solution with push to talk on the handlebar. (Radio ~$30, wiring ~$35)
Radio :
https://www.amazon.com/dp/B007H4VT7A/re ... tBbDXYVQKE
Push to talk / radio harness :
https://www.amazon.com/dp/B019YJMRZS/re ... tBbJ104JRN
Helmet speakers / boom mic :
https://www.amazon.com/dp/B01LSH3KQY/re ... tBbPDFM74G
3.5mm 3 conductor extension:
https://www.amazon.com/dp/B07DLSB9KY/re ... tBbHKKN0Z3