An additional radio would raise the price of your phone for at least another 200 or 300 dollars. Try to enable VoLTE if available for your operator. That makes the phone use the LTE connection for voice and don't drop the Internet connection while you talk.
Dual SIM Dual Active phones are under £100 in the UK, I imagine under $100 in the US.
Dual SIM Dual Standby (two or more SIMs, one radio) is cheaper, less battery, less space, and usually good enough. It's literally a few dollars, not 200-300.
The chips cost under $100 even for top tier modems from Qualcomm.
You can get an additional phone with a screen, 5g radio, ram and everything for $150. An additional radio should not raise the price for another 300.