SparkFun Electronics is offering a web based custom board design service called SparkFun A La Carte (ALC). You can choose from a few different microcontrollers that can run Arduino programs. You also have a choice of I/O, connectors and power options. Communications options include RFID, WiFi and Bluetooth. There is a one-time design fee for each board and a per unit cost calculated as you add the components. You can get a 50% discount on the design fee until 12/31/2020 with the promocode ALCSPARKFUN50. For more information see this ALC post on the SparkFun Blog
This YouTube video on the custom board designer goes over an example design.
