you can make it as cheap or expensive as you want it to be. A big expensive one I'm sure would be better, but you can still be well-served by a £2 usb dongle off wish.com

You drank the aptX kool aid and forgot the fidelity loss along the signal path.

FM broadcasts do a high pass at 50 Hz and stop at 15 kHz. The best SNR is only ~50 dB which is already achieved by plain old SBC. There is no need for higher fidelity audio codecs like AAC/aptX/aptX HD/LDAC besides the fact that most smartphones don't support aptX or aptX HD.