The T3i is a noticeable upgrade from the T1i. There was a substantial sensor upgrade when they introduced the T2i. The T3i added the articulated LCD as well as allowing the onboard flash to act as a commander for off-camera flash.
I've noticed that when a product is discontinued, some retailers will set a particularly high price tag on the item. I'm not sure if this is a "nobody else will have this and if there is a reason you specifically need a T1i vs. any other camera then you're going to have to pay our premium" or what... but I have noticed a trend that products no longer in production initially go way down in price... and then after a while the few places that claim to have them shoot the price way up.
Regardless of the prices you can find online... the T3i is a better camera. Enjoy your T5i.