[support] Views Output as Link/Custom Field Handler

[DTH]

In my view I have a number of fields. One of these fields uses the
Output As Link option. This works fine. However, I only want it to be
a link if certain criteria is met - so, for example, if the field
"sold_online" is true, then the field "price" should be a link to the
online shop, while if "sold_online" is false, then the price should
not be a link.

What's the easiest way to do this? Write a custom field handler that
extends what? Is it views_handler_field_url? In a custom handler, how
do I check for the value of another field (assuming "sold_online"
comes before "price" in my list of fields)? Or am I barking up the
wrong tree and there's something much simpler I should do (for
example, using theming?). (And is there a handbook page or anywhere
where you can find a list of other people's custom view handlers?)