I have to agree with Jason.
On some (perhaps many) casting kits I have seen, many of the parts are more like blobs of cast metal, with little in the way of detail.
I saw a discussion on another forum the other day about how it is getting more and more difficult to get foundry work done for model engine casting kits.
One of the reasons I learned how to cast gray iron is so that the technology would not be lost to the model makers and others who may want to use it.
As far as cost, I have not really kept up with it, but a few costs are as follows:
(prices are so volatile now that I am not sure how accurate this will be next month)
1. Two bags of Mizzou refractory, perhaps $275.00 shipped
2. Two Sonotubes, $25.00.
3. 2.5" muffler pipe, $12.00.
4. Spray nozzle, $30.00 shipped.
5. sheet metal exterior (used 55 gal drum), ?
6. Miscellaneous bits, steel pipe, fasteners, etc. $100.00
7. Clay graphite crucible, $100.00 shipped.
8. Plastic fuel container $25.00.
9. Fuel line, $25.00.
10. Air line $20.00.
11. Scrap gray iron, one place priced it at $0.40 per pound. I found some motor end bells for free.
12. Metal to fabricate lifting tongs, $25.00.
13. Metal to fabricate pouring shank, $25.00.
14. Metal to make ingot molds, $25.00.
15. Wood to make flasks, $50.00.
16. Foundry sand, depends on what type you use, perhaps $0.20 per lb.
17. Fuel cost, I run diesel at about $3.50 per gallon, burning 2.7 gal/hr, with a melt generally being 1 hour.
18. I have an air compressor, but if you don't have one, you have a few other options.
I did build my furnace and burner to last indefinitely, so spending a little more money initially pays off in the long run.
So adding all the above costs (not including labor), you could build a very nice iron furnace and diesel burner for probably under $1,000.00 US.
I paid $600.00 for a single casting kit (ball hopper monitor), and so you would not have to buy many casting kits in order to make your own foundry.
Of course some would pay good money not to operate a foundry; it can be very hot and dirty, but that part does not bother me; its about saving the technology and preserving it for future generations.
And I love to make my own iron castings, just because I can make castings that cannot be purchased anywhere in the world.
Here is the 3D printer filament that supposedly burns out cleanly (I have not tried it).
PolyCast™