If all you want to do is try and save money by casting something that is already available, you'll soon find that it does not pen out, unless you need many many of one particular part, but then again, if you need a bunch on one item, maybe you should call the people that make the part(s) and ask about quantity discounts. Also, I believe that Precision Scale Co. will make castings of your supplied original part (but they won't make something from a third party of course).
Learning new skills for modeling is good. I'm learning to etch metal to make scale spikes, tie plates, etc. for my 'in the planning' HO layout. I use some of the new proto87 parts but they are designed to be glued together and I believe I need to spike everything just like the big 1:1 scale versions do, so it's off developing my own kit. Good luck if you decide to learn casting, it's non trivial and requires some sophisticated stuff to turn out consistent results.