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 -> 1/2" BSPP Male | $11.66 | Ebay
Adapter | SS304 | 1/2" BSPP Female -> 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 -> 3/8" NPT Female | $ 5.00 | Grainger
Adapter | SS304 | 3/8" NPT Male -> 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 -> 1/8" NPT Female | $ 5.00 | Grainger
Sensor | SS304 | 1/8" NPT Male | $20.00 | Ebay
Total $28.00