Unless you even larger coils you better hope for txvs because in order to meet minimum efficiencies you have to enlarge the coil more for a piston.
So whats the cost of a larger coil? Well obviously more material. Oh and heavier, and less on a truck, and more refrigerant, and tougher matches when it comes to hp's and poorer (is that a word) latent capacities and, difficult retrofit, the list goes on. Who's going to pay for all that stuff? An OEM TXV will probably allow the minimum efficiency at a lower cost in the long haul but hey if your hung on just the price of the part then so be it but ultimately it will not cost less but more.