I have a few different systems, and they all have different I/O devices. My main box uses a Kona 3. Certainly not in the “cheap” category, but perhaps one of the best alternatives, if Avid is your only concern.
I Have a Matrox MXO2 which I used to use with an older Mac Tower. It has since been relegated to “if I need something on the road” status. Works quite well, and has a nice form factor with Analog and digital ins and outs, and can be hard wired into a desktop, or slide into a PCMCIA type port on a laptop. I just discovered the drivers for it are not compatible with Avid 8.3 yet…so be careful.
The reason the Mxo2 was relegated was because of my need for Black magic devices to run as well, so my Mac tower currently has an Extreme 3d from Black Magic in it. Again, pretty much every I/O type you could ask for. No longer sold however, and again, not cheap…pretty much the same as their high end 4k card.
(4k extreme)
My main box (with the Kona) also has a BlackMagic 4k capture card in it. It is the Decklink SDI 4K..about 180.00 or so? I need it more for monitoring out of Resolve (and now fusion..which seems to have lost its Kona ability with BM buying it!) but I see no reason it wouldn’t work for ingest as well.
My latest is a Black Magic Mini recorder. Got this off Ebay for a pretty reasonable price. It will probably come on the road with me next time. I’ve used it for a test only on my HP Laptop. HDSDI in and then connects to the laptop with thunderbolt. The test I did worked well, and it is very small for portability. It doesn’t have machine control, if you would need that, so it is definitely geared towards a specific userbase.
For proper machine control, I would try Kona, MXO2, and then one of the BM cards with that function attached. They all play nice with Avid, but only the BM products will work with Resolve as well, if that looks to be in your future.
Glenn