A programmer's time is worth at least $20/hr+.
A decent script will typically cost a few hundred dollars, depending on complexity of the method.
Just some estimates here, I don't know the market super well.
Smithing seems to be quite simple, maybe $150-$300
A green dragon killer would probably run you $400+
Highly depends on features needed, complexity of method, etc.
You'll definitely get your moneys worth and quality work if you select a talented scripter!
Plenty of people have purchased private scripts and profited greatly, just need to be smart about your method/investment.
You can make a request/find talented scripters over at TRiBot:
Requests