That's a tough question to answer but the good part is that it can easily be done on a small scale and expanded as your budget fits.

I started mine for a little over a $200 at first. However that figure does not include the cost of artificial lighting (my system is indoors).

There's various ways you can build the beds, fish stocking tanks, filters.

Also used equipment can be purchased fairly cheap. I recently picked up a 90 gallon pre-drilled aquarium and 10 gallon fish tank for $60 off someone craigslist. It's going to be my breeder tank and I used the 10 gallon as a sump filter.

As Keith said IBC totes are a good way to start. The give a good amount of space for your fish and provide 1 grow bed if you cut the top of them off. It's a popular setup. I found IBCs around $175-200 a piece around me.