Arduino boards are fun to play with and they will likely have a major role in this project. USB based boards start at about $35 if one buys an original. Fortunately, there are a number of other hardware options, that work with the ingenious Arduino software, such as:
These all require the FTDI USB to TTL cable (only once for about $20) and some soldering.
If you don't mind the RS232 interface, you can go with the serial Diecimila board or build your own Arduino compatible board. This is what I did, as I already had an AVR-P28 from Olimex and an ATMega168-20PU chip, plus a 16MHZ crystal.
Simply connected pin 2 and 3 of the chip to TX and RX on the board so the microcontroller is connected to the serial port.
The board is really helpful in writing the Arduino bootloader on the chip. Once it is done, the board can accept code from the Arduino software. I found, that in is less seamless then the factory USB arduino. The upload and the reset button on the board must be pressed almost simultanously to get a successful upload.
I have also added 2 female header boards, that can be seen on the above pictures. Those are optional of course.
The RS232 port already on the board will come handy when interfacing with the SportIdent serial main station.