IMHO , can purchase sand at ah beng at $2 per kg loose . As per mentioned by other seniors , regular water changes is sufficient if not running skimmer .
If wana save on test kit , perhaps can run longer cycling period just to be sure as test kits are not cheap ( at least to me) .
For salt mix , if lower budget can get nsw for water changes instead ( me) .
Dosing I feel depends on wat corals u keeping and honestly without proper filtration and gear , max is prob simple corals like zoas etc so quite redundant ( again , my own opinion) .
Food wise , corals that does photosynthesis does not require feeding but it's good as a supplement .
Was told fish poop = coral food ( duno how true is it) so feeding the fishes will be ur key concern .
I feed mine with frozen brine shrimp and mysis which I use as well to feed some of my corals .
Hope it helps as I'm new as well.
Cheers