If you're looking for something cheap for testing, Nexcess has shared accounts starting around $25 per month, as well as cloud accounts starting around $49 per month. Magemojo has starter plans around $98 per month. Plans like these may not meet the needs of for the live sites of established businesses, but are likely to do the trick for what you've described... and they're supported, letting you focus on dev, as opposed to hosting configuration and optimization.
James Lee, who responded earlier, shared a link in his comment that includes several affiliate links. This includes Aspiration Hosting, which he founded. I'm not a fan of affiliate links, and I'm not sure if moderators will leave his link in his post as commercial advertising is usually scrubbed from these forums, but hopefully, as a Magento Master and founder of a hosting company, he's shared some good ideas.
Best of luck!
