I want to know if there any good lumen meters available, Or if those are only for labs.
Is there any good way to measure lumens without a specialized meter?

Look for "Light integrating sphere".
"Lumen meter" is a sphere at least 20x larger than the device measured, with a "lux" meter and recalculation of the result (for the exact calibrated parameters of that sphere).
So pretty huge equipment.
The sphere you may build yourself: Just an inside white (the TiO2 white is one of the best coats for a visible spectrum) hollow sphere, the luxmeter uses difusor (a small, the same white coated, ball obscuring direct light from the measured source).
The DUT is in the center, if you are only about to measure the classical LED's (emitting only in one half space), it could be in the sphere wall (a bit simpler, mainly with smaller size).
Then calibrate it using some known light source (for relative measurements the "lux" value is way sufficient).

But is the spectral sensitivity of cheap meters really same as in the definition of the photometry units ?

But is the spectral sensitivity of cheap meters really same as in the definition of the photometry units ?

Within their accuracy specification...

CdS matches the vision characteristic pretty well, but the general sensitivity tends to long term drift over time.
Semiconductor sensors are worse, mainly because you don't exactly know what the sensitivity shape really is.
Of course, the best is a calibrated spectrum analyzer and then an (Excell or so) math, but that is more difficult to get, although many DYI designs are around - mainly the ones using CD as difraction grating and then some camera, all the setup then relatively calibrated using a regular incandescent lamp (the incandescent provides well defined accurate reference spectrum, the only thing you need to know to put as a parameter is it's temperature)