I have to modify an existing electronic cashier that use RS232 to connect between the computer and the money tray. When the user press space on the computer, COM's DTR is set to and hold high for a short period of time. The tray automatically open using an relay. Due to high current pass through the relay, the tray got an external power supply.

Now I have to change the connection between the computer and the tray to USB. After some searching on the web, I decided that using an usb-rs232 virtual com (SiLabs CP2101, FT8U232AM...) would be the easiest way. Unfortunately no electronic store in my city, and probably in the whole country, got those parts. I have a quote for 1000 CP2101 on nowcomponents.com and they came back with 115U$ for a chip. The evaluation kit on SiLabs website only cost 49U$!

I got an application notes from atmel using AT90S2312 as RS232-USB converter but I think using an AVR is overkill in this case. And this MCU is also not available in Hanoi.

The questions are:
1. Am I on the right track? Since I only need 01 pin in the RS232 side, is there anyway I can do without an MCU?

2. How can i get a more reasonable quote? The quantity I want to buy is from 1000 to 5000.

In case I forgot to mention in my profile, I'm in Hanoi, Vietnam.
Thank you.