for want of a nail, the kingdom was lost....
for want of a dust seal and some grease, the pedals were lost.....
IME, (just like headsets, BBs, hubs and freehub bodies) if you don't maintain pedals, then they tend to fail, sometimes rather quickly. This leaves you
a) with a bike that is broken and needs repairing, probably at a time that is not of your choice
b) shelling out for another set of pedals
c) with a repeat performance guaranteed at intervals of a year or two, as long as you carry on cycling.
d) needlessly contributing to the appalling waste in our 'throwaway society'
New PD-M324 have a RRP of about £50. You can get them cheaper than that, but that is what you will pay as a 'distress purchase' in the event that the pedals fail and you have to get another set from the LBS in a hurry.
I learned my lesson years ago; I bought a cheap set of pedals and had them on my training bike. The pedals were not assembled well in the factory plus I abused them. Less than a year down the line the pedal bearings were slack, rough, and had clearly had the weather inside them. At this point I wondered if it was worth doing anything with them, 'because they were only cheap'. I ummed and ahhed about it and I grudging (it was dark, cold and threatening wet at the time, and I had to work outside) set to. I found that there had never been the correct quantity of ball bearings inside the pedals. I rectified that, installed better seals, drilled a lube port in the pedal body and put the things back together again.
Thereafter the pedals needed adjusting about once every six months for the next year or so, then much less frequently. Maintenance consisted of adding grease through the lube port and wiping the excess away. It took half a minute to do that, once every six months or so.
I ended up using those pedals for about twenty years. Towards the end the outsides looked as if they had been in the sea, but the bearings were unbelievably smooth (they just got smoother and smoother as time went on), and they hadn't needed adjusting for several years. Actually I retired those pedals in favour of some different ones, rather than because they were worn out. Goodness knows how much longer they would have gone on for.
Potentially they saved me at least ten pairs of 'cheap pedals' plus whatever breakdowns I'd otherwise have inflicted on myself.
It really does not take long to maintain pedals, once you have set yourself up for it; correctly adjusted and lubricated bearings need adjusting far less often than the other sort, and a lube port makes relubing very easy.
It really doesn't matter how much your pedals cost, when they break it is a major PITA.
cheers