I installed one on my Yaris, with the same 1NZFE engine as the Echo. There's a machined hole on the back side of the engine block or cylinder head where you insert the block heater. One simply inserts the block heater into the hole until the locking tab clicks. Then just run the power cable out the front.

If you're mechanically inclined at all, with no freeze plug to remove and no coolant to drain/refill I wouldn't pay someone $100 to install it, if you've got the time and patience to route the wiring out to the front grill/hood you're better off doing it yourself.

There are a couple of write-ups on Yaris World : http://www.yarisworld.com/forums/showthread.php?t=23021

 

Did it myself for my dad Echo 2004, bough the heater and cord from Toyota, they also included some conductive grease to apply on the element so it transfert heat better to the engine block ! took an hour max.

From the top of the car you need to reach rear of the engine block to find the hole with your fingers, before applying the grease to the element and put it in with your other hand. Don't forget to plug the wire on the element BEFORE putting the heater in !