tellermine are costly(and only pionner can put them) this early since usualy you battle for fuel and wont be sure to get ammo as ost. and pak40 isnt the cheapest/most sturdy AT alternativ, its good as its reliable(in penetration at leas) but it certainly can't afford to be spotted
they indeed arrive soon they just are very costly and require or a bit of luck(tellermine arent auto rolled upon) or good micro ATG needing a good placement to both have a good line fo sight and be far enough to not get rushed.
panzershrecks arrive way later(and arent even good, sicne their so squishi)... if you can panzerschrek you already have quite a fuel advantage on your opponent.
You asked for a counter to early light tanks in which case a 50 muni teller mine is nothing compared to the price of say a t-70. The pak40 is one of the best AT guns in the game and for 100 munis you get double panzershrecks on a squad of panzergrenadiers which will absolutely annihilate a light tank.
I would be hard pressed to think of another faction who is more capable of countering light tanks. Brits struggle against this waay more for example, as do USF unless they rush captain.