I run an old wire in Link plus in my starlet, sure it's not the flashest piece of hardware out there but it starts well and drives pretty nicely, with decent economy...
Just remember the ability to tune and monitor you engine will make or break the whole car..
Sure it possible you could do what steve is suggesting but until I see him build a "hotrodders" efi lawnmower controlled by a a late model evo ecu copmplete with obdII wiring to check for fault codes i'd steer clear of that option.. You'd end up bald/grey haired/both before the thing ever got running.
Link is a good value for money product, the support is just a phonecall away. You could try and save a few bucks and pick up a second hand unit and get it upgraded?
If you go down the megasquirt route I think you'll need to be near the top of your game to end up with a unit that will work as well as a link..
the only expericence I have with the MS is a good one.. Although it came from someone whi is very proficent in the backyard mechanic game..
Wiring in your own link or building your own MS is not "chequebook" racing as far as i'm concerned..