I just installed a Scan Gauge II and highly recommend one. I previously installed sending units in the test port on older Ford trannies (E40D/4R100) and ran Autometer gauges. More work to install and you need a place to mout each gauage, ec. trans, water temp., volts, etc).
Now with the SCII and have 4 gauges reading at once!
The install is very simple. I would also recommend the Blend Mount to mount the SCII over the rear view mirror/ It works prefect and was also easy to install.
I can't imagine the cost exceeding $150 to install both the SCII and Blend Mount. The only work here is running the SCII cable under plastic trim above windshield and over to left, and behind the A-Pillar plastic trim on down left side of windshield to under dash and to OBD port. It took me about 1.5 hours to mount, run cable, and program trans temp.
Here is where I purchased mine:
Scan Gauge IIBlend Mount BSG-1000