Snake, metal injector syringes are the way to go and they cost less than 50 bucks through Bear, Jacobs or Lurecraft.
Just remember to use rubberized fishing gloves when handling the syringe for multi pours. The metal gets a might hot.
Easy to clean (pop out the blob left inside) and start again.

A glass candy thermometer works fine and costs a few bucks. I've had mine for five years and it goes to 400 degrees.
Temps over 300 read in about one minute. I keep my plastisol around 300.