The TEMS cost me $50 each as well becuase I bought them all at the same time along with some other parts. Toyota list price was around $72 ea.
Lowered springs cost nothing because they were on my car when I bought it! In fact, I had to put the jza70 struts in to pass rego inspection as with the lowered/aftermarket ones they couldn't get their jack under the car! That said, someone is selling a set of Kings springs on the forums pretty cheap. So you could do a suspension unpgrade for less than $500 on the cheap!
Get a new wheel alignement too - the Supra's are totally adjustable and you'll need one if your lowering the height of the car.