Hello there, this is my first post, so please don't hurt me
The biggest problem with any creative work (copywriting, web design, graphics design, programming, etc) is that it is so ambiguous in terms of time frames and costs.
The hardest part of being a programmer is that it's impossible to tell people how good you are. Your client has no idea how to program and its really difficult to quantify.
With web design and copywriting there is an answer however. Things can be quantified using google analytics (or alternative). You can actually show measurable return.
The hard part is starting out and getting to the stage where you have documented provable return on investment. The only way is hard work.
If you are good at what you do, if you can show Return on Investment, you can charge more than the next guy who can't do that, plus get the job over them.
I guess what I am trying to say is that....the market for good copywriters will never dry up