Adding UART to RS-232 converter on existing PCB

We want to find the lowest-cost solution to convert our UART to RS-232. There are many chips but most are very expensive or not available. We are planning for 10,000+ units/year so we need a cost-efficient solution. The job would involve selecting the best components then updating existing schematics and layout in Altium. Please tell me what is your experience with RS-232 and what you expect the components cost for this feature would be.
Thank You !