Haltech is a good option, however there will be the added expense of having it wired in. The closest to a plug in solution from haltech would be the Platinum sport 1000 and the ST185 celica patch loom. Being an ST185 loom, it is closer to the earlier SW20, so some repinning would be required to make it a viable option. If it can be, you would have to consult someone more familiar with the gen2/3 stuff than myself.
http://store.haltech.com/default/plug-n-play-ecu-kits/sport-1000-patch-harness-kits/ht-051360-ps1000-patch-loom-kit-toyota-celica-gt-four-st185.html Its also $1895. Making it the most expensive option. Also requires mounting the ecu, for proper operation would will also need to put in the air temp sensor.
http://www.linkecu.com/TST205Plus The link is to suit your model. You pull apart the stock ecu, change the board with the link one, make somewhere for the tuning cable to come out of the case, put it back together and off you go. Can have a knock link added for knock control functionality.
Then power fc's will be the cheapest option, and for pricing your best off speaking to gorilla industries, or see when one pops up on the forum.
But as Steve A has rightly pointed out, sometimes the best option is something your preferred tuner is most familiar with. Most tuners aremore than capable with power fcs, then some will like links over haltechs and vice versa. Also workout your budget, as that will dictate a lot, as the price difference between a power fc and a link/haltech will be most likely $1000, and then more again in the tuning (as there is less setup and adjustments to make in a powerfc)