I don't know very much about this...others will know much more.
But, I know that I am still using a pair of SPD compatible shoes I got for about $45 (on sale from about $60). My pedals were something like $80.
Now, do I dream of much nicer, lighter, more comfy shoes and pedals? Yes. But, really, so far so good with these. I can do 100 miles in them, and I can do long 12 hour climbing rides. No major issues.
I'll upgrade when I can, but it won't be because I have to.
That said...I have found in biking that it works for me to get the good stuff if I can, because later I (1) end up wanting it and (2) end up building my skills to the point where I can tell the difference...
"The best rides are the ones where you bite off much more than you can chew, and live through it." ~ Doug Bradbury