I think for a complete unit the Computec and Racedata are competitivly priced.
For Sensors..I like all of them... the more the better... but I pay attention to the following
Engine RPM
Drive Shaft Speed
EGT
Water Temp
Oil Temp for the Transmission
EGT- just for basic tuming
RPM and Drive shaft speed - Tire spin and it allows me to keep an eye on the transmission/convertor
Oil for the Transmission just to keep an eye on it for maintence
When it was 1st installed it was a great toy to have. When we started struggling with keeping the car consistant (kept adding more power to run the #) The sensors showed the transmission starting to slip ...Heat started going up higher and Engine RPM was not creating the drive shaft speeds we were used to.,
On the TD car it was showing us that we were running out of fuel at the 1000' mark.
They really just become another tool you use, they help in set up, tuning and maintance. The 1st year we ran alcohol injection and went to a differnet track we would change the pill on what we thought it should be, after the first pass with the EGT we could make the 2nd change and would end up seeing thee EGT that we were looking for