It depends on what you think is expensive or cheap. $70 for a laser power meter is cheap in my book, but this is very limited in power handling, and i'm not sure about accuracy. It also is a retail price, i'm sure the total cost of parts for that meter are much lower than $70.
I think that the LPF commnity would mostly like to see a LPM that can handle more power, ideally up to 10 or 20 watts. It would be a challenge to find/build any affordable sensor that even survives that, but it's a goal that can be worked towards.
TEC's seem like a logical choice here since they are at least available at such power levels, but you cannot just point a 5 mW, 5 mm beam diameter laser at one, that will probably burn the surface.
What could work in my mind is getting the tec, and affixing a layer of anodized aluminium on the side that takes the laser light. This could be something the size of the tec, and perhaps 0.5 to 1 mm thick. This adds a LOT of thermal mass to the system, and the only way to get such a system to respond and acceptable speed is to use a power-following, unlit, identical tec heated by a resistor.
I'll be abroad for a well over a month from xmas and will not be able to do any practical work on this, but i could after. If you have any good options for the TEC or anodized aluminium material in mind i'd love to hear details.
Actually i am using a .5mm sheet of copper and wrapped the resistors to it and glue it with thermal paste onto the tec ! As i said i need to conduct tests in the coming days !