Your biggest cost for a parlour is the equipment: stainless lines, pump(s), holding tank, pasteurizer/homogenizer, gates/parlor hardware, etc. The container is nice because its modularized and potentially portable. But if you don't need it to be portable, then a regular barn might even be cheaper. Last time I priced it out, a used insulated container here by the port was about 3,500-6,000 USD. That's likely cheaper than what you have because there is a surplus of containers here as I have two large ports nearby. For that amount, I can build a good size barn. Of course, if portability is needed, such as if you're doing intensive rotational grazing, it may make sense to build a completely portable parlor.. but with 8 cows its easier to bring them in.