Hey man... I don't know where you are looking for meters, but they ALL have ppm.
I looked at DiscountHydro.com (not where I shop, but a populart site). They have 12 different meters and every single one of them measures ppm.
I'm not really sure what you are talking about, but I think you are just mistaken. They all (or at least 95%) have ppm readings.
Just decide how much you want to spend and buy one for that price. The more you spend the better meter. The less you spend the faster you are going to need an expensive meter to replace the peice of crap you just bought.
I don't know if anyone is going to tell you an exact meter to get except a salesperson, and they will just tell you to get the most expensive.
The pretty much are all worth what you spend.
And also, I think between the temps and humidity that's a tough environment for clones/ new plants. Maybe cut one of the lights off till they are bigger??? Or even two of the lights???
And humidifiers are cheap and easy to run... it's the dehumidifiers that get expensive and a pain.