Accessibility testing on a budget
Accessify's favelets
Among the other free tools available on this site, the favelets will probably be of most interest. They have been specifically written to highlight potential accessibility problems or oversights.
The images alt attributes favelet looks at all the images on the page and displays them in a new window, alongside the alt attribute. This may seem simplistic, and you may be asking yourself "what's the point of it?" given that Bobby and other online tools can highlight empty alt attributes. The point is that these automated tools cannot tell you whether the alt attribute is correct. Using this favelet you can quickly scan down the list and see whether the alt attribute matches the image.
The missing alt favelet is similar to the above, but only picks out images that have not been given an alt attribute.
The link titles and href favelet shows all links on the page (only true <a href>s, not elements that are linked using an onclick event) - whether they are text or image links - alongside the destination URL and any title attribute. You would use this to ensure that the title attribute matches up with the link text and destination.
There are other favelets available on this site which you may want to look at too.