What is the engine that is currently in your car?
Is it st gt gts or alltrac?
279,000 miles is a lot on an engine.
The 1.6 liter is very easy to get ahold of, you can get them from a gen 5 celicas(that's your car model) or you can get them from a camry. I endorse the 1.6 because it is small and very easy to handle. I see these engines on ebay. You should buy it from there and let us know how it turns out. They are like $700 shipped.
I have the 1.6 liter engine and have 220,000miles and have had no problems and it has retained it's power.
It's also a lot on the tranny too. If the sincros are bad use syncromesh fluid by pensoil it makes the tranny knew, I am assuming it's manual.