Built my first website at the age of 12 on GeoCities and my passion for online technology has not dimmed at all since. Graduated with a BA in Graphic Design with concentration in Art & Design to pair my web development skills with web design skills enabling me to design and build highly functional websites. At the age of 24 became Co-Founder & COO of PageLadder, Inc a Inbound Marketing company focusing on bridging the gap between sales and marketing. I'm now soon to be 28.
Having an online portfolio is important but even more important is that you have reviews. You can put them directly on your portfolio site and they will act as 'social proof' enabling you to convert more jobs. Since you say that you've worked with computer graphic for years I assume you've done some work for clients. I bet in your e-mail you have these reviews just sitting there hiding from past clients or even associates or friends who have complimented your work. Publish them out there for prospect to see.
My portfolio is pretty weak relatively I think but more than anything when I link people to my reviews on codeable or my linkedin profile they instantly trust me and pull out their wallet :)
Outside of that another tip would be to specialize. There are lots of Graphic Artists out there you need to specialize and differentiate yourself. There are many really talents Graphic Artists out there who are successful without having a degree so don't let that hold you back.
Hope that helps. Cheers - Raleigh
Sounds like you are playing the role of the web designer and web developer in those situations. If you consider yourself very very good with UI UX design people are willing to pay big bucks for quality work there. As far as the development side it's more about the timeline for development and how many bells and whistles. I've worked with small to medium sized businesses and do not think $250/hr is unreasonable or unusual for top quality design and development on a normal timeline.
Happy to discuss more just wanted to get my thoughts out to bring a bit more perspective in.