After doing much research recently as I need to get an LPM myself, I would personally recommend a LaserBee outfitted with an Ophir sensor head. Response time is a only few seconds, can measure up to 20W for a duration if heatsinked well, and you'd get the data logging software via the LaserBee unit. Considering it is an industrial grade sensor head, you probably won't ever need to buy another LPM in your life.
The cost is something to be worked out with Jerry
@lasersbee though...
He could probably set you up with just a LaserBee unit without a sensor for discount, and then you could get a used Ophir head for maybe $250. All in all, the most you'd
probably be looking at around $350-$400.