Cheapest way of adapting G1/4 sensor to 1/2" NPT
O.P. here. I found NPT sensors on ebay for $8 more than BSPP sensors. The amount of money to adapt BSPP to NPT would cost more.

BSPP Sensor Method #1:

Tee     | SS304 | 1/2" x 1/2" x 1/2" NPT Female        | ~$ 3.00 | Amazon
Adapter | SS304 | 1/2" NPT Male -&gt; 1/2" BSPP Male      |  $11.66 | Ebay
Adapter | SS304 | 1/2" BSPP Female -&gt; 1/4 BSPP Female  |  $12.20 | Ebay
Sensor  | SS304 | 1/4 BSPP Male                        |  $11.20 | Ebay
                                                    Total $38.06


BSPP Sensor Method #2:

Tee     | SS304 | 1/2" x 1/2" x 1/2" NPT Female        | ~$ 3.00 | Amazon
Adapter | SS304 | 1/2" NPT Male -&gt; 3/8" NPT Female     |  $ 5.00 | Grainger
Adapter | SS304 | 3/8" NPT Male -&gt; 1/4 BSPP Female     |  $15.00 | koolance.com
Sensor  | SS304 | 1/4 BSPP Male                        |  $11.20 | Ebay
                                                    Total $34.20


NPT Sensor:

Tee     | SS304 | 1/2" x 1/2" x 1/2" NPT Female        | ~$ 3.00 | Amazon
Adapter | SS304 | 1/2" NPT Male -&gt; 1/8" NPT Female     |  $ 5.00 | Grainger
Sensor  | SS304 | 1/8" NPT Male                        |  $20.00 | Ebay
                                                    Total $28.00