Lapizuli - 6:51 pm on Apr 23, 2010 (gmt 0)
You have more freelance experience than I do - I started in fiction, so I don't know if this can help. But...
Have you already considered oDesk or eLance? They handle the payments and have an escrow-like system for making sure payment is made for the work you do. Although they take a cut, it's not very large. Plus it's simply easier to find clients through them. You can apply for specific contract work, or they can find you. I found a nice client through oDesk when I went semi-freelance last year. If I were still doing freelance work, I'd do it that way. It really is hassle-free.
If you already have enough momentum and contacts and whatever to be confident in your client base or just really want to go it on your own, I recommend you ask for some money up front. You could ask for a good faith 50-100% payment for the first job. You can state that it's negotiable under certain conditions. You can say that after the first job, you work out specific custom payment arrangements.
When you're starting out, you want to leave yourself open to case-by-case adjustments because you may not get the clients, otherwise - and also because each client and each job really is different. But nobody legit will have a beef with your asking for some up-front payment if they can see samples of your work and trust from your website, professionalism, and samples that you'll write reliably and well for them.
Regarding prices, I suggest you leave it wide open, yet provide cost estimate guidelines so they come to you with a realistic idea of what you charge - something like:
"Terms will depend on the specific job. Sorry, there are no volume discounts. [examples here of what cost depends on] Generally, I charge:
X$-Y$ per 400-600-word article for SEO article writing that requires little or no research (give example)
B$-C$ per 400-600-word article for SEO article writing that requires significant research. (give example)
Z$-A$ per 2000-word landing page
You asked how much you should charge. For article writing, you'll have lowballers wanting to pay you very low amounts per article. I can't say for sure what "low" is, because it depends on how much work is required and how good you are, etc.
Some would consider $1-$10 per article extremely low and even $10-$20 ridiculously low, while others would consider any job worth it. Yet most likely work won't be thick on the ground for more than $15 per article until you build up something of a reputation, find a good client, or have something spectacular to offer - such as testimonials or statistics showing you've increased a client's profit by such-and-such amount.
Many writers moving from traditional print publishing to online publishing take work very cheaply at first, then quickly are able to charge more realistic and even traditionally-structured prices.
The more you do it, the more you'll get an idea of what's worth it to you. I suggest you go with what's most comfortable for you, then loosen or tighten your restrictions as necessary. I wouldn't worry about making a mistake. There's a huge demand for writers right now. Many don't know it, because bad writers are everywhere, and everyone thinks they can write well enough, and there are tons of print writers out of work. But it's all an illusion, and you've got a lot of leverage here.
Hope this helps, even though I have no solid numbers for you. Good luck!