I'm currently searching for a way to get 4 channels of audio from mic level (XLR input) into a Raspberry Pi. Either as a single interface device or one channel and use four of them. It only has to be something simple as it will be built into a casing of a bigger product. Price is definitely a point. I'm looking for something in the sub 60$ range. Ideally it would have an XLR input, Phantom Power (doesn't necessarily have to include that), gain and USB-Connection to the Raspberry built onto a circuit board. But jack input would be fine as well.
I would advise you against your own hardware for this task. The goal of Raspberry Pi is to be a small-size substitute for a PC, not a large-size substitute for a professional recorder.
Based on your comments, you have some quantity of XLR microphones—you weren't clear if it's two stereo microphones or four mono microphones—and you want to mix this sound and stream it to the web.
With a Raspberry Pi, you'll have three limitations:
Connectors. XLR connectors are quite specific, because of the constraints of audio signal transfer. While XLR to USB adapters and cables exist, it will have its negative consequences if you require quality sound, and it possibly won't have the features of standard XLR (possibly no phantom power).
The fact that you want to install it into a rack makes things worse, since you possibly won't be able to use USB connectors, and would require to make your own connectors, somehow. Unless you have experience with that, here again the audio quality will suffer.
Performance. Raspberry Pi is a nice and very capable machine, but if you want to process and stream sound in real time, it may quickly become a limiting factor.
Software. Things as simple as adjusting the levels of the individual microphones or visualizing the levels to check if they are set correctly would probably require either to develop a custom script or to install a custom software.
Instead, you may purchase either a mixing board, or grab an audio recorder. Zoom H6 could be a good idea; while it costs around $300, you may take in account that a Raspberry Pi, the XLR connectors and the custom rack enclosure won't be cheap either.
Another choice would be to use Zoom H5 with a EXH-6 Dual XLR/TRS combo capsule if you have four XLR microphones, or just the recorder without the additional capsule if you have only two stereo ones for about $160 used (or $210 new). Or you can look for older models, second hand, which may be found for a price below $60).
A few illustrations of Zoom H6: