The cheapest and more efficient solution would be buying a buffered serial port that connects to the clockport. The PortJnr for example does the protocols in hardware. It's not that cheap for what it is (just a serial port) but it's very cheap compared to other solutions. If you're persistent you can't find some in the second hand market.
A BVision Gfx card would make a big difference to your system though and you can get them like already said for around 50£. Although this would apparently require towering and so more money I've hear people haing it in A1200 desktop cases.... beware of temperature problems , be sure to have the necessary cooling..
