Are we talking about a mains powered circuit? Please specify input voltage range and output power.
For mains powered flyback converters, take a look at the TinySwitch series from Power Integrations. They tend to be
fairly cheap.
I think the biggest cost is going to be sourcing a switching transformer to go with it. Those are usually custom wound for the job, so finding the right ones in low quantity is going to be a bit tricky.