Industrial RF replacement for Xbee based UART communication
If you're designing for higher quantity or commercial release, you will be facing one big problem for rolling your own RF solution: compliance. Even though most electrical and electronic regulations are voluntary or self-certification, anything RF quickly needs to be FCC approved to be sold at all (assuming you're a US person). This is why it's actually a good idea to stick with a ready-made module. This way you can rely on the certification and compliance testing that they have already done.

Of course, this still means a lot of vendors remain. But I would definitely recommend sticking with complete modules instead of trying to build your own. They are slightly more expensive in quantity than for instance an nRF24L01+ solution (currently the lowest-cost fairly robust low-data rate RF solution on the market), but you don't have to go through expensive audits and tests.