Sand is great.
garnet sand.
black diamond sand.
pool filter sand
play sand.
<$10 for 50 lb.
Disadvantage:
Your motors can grind (annoygingly loud) or completely jam if sand gets sucked into the motors.
Make sure you use a short intake pipe, well off the sandy floor. Perhaps a good 6" off the floor at least?
Advantage:
Much less waste and ammonia build up.
Poop sits on the sand surface, either gets eaten by other fish, gets sucked into the filter, or easily surface vacuumed out. No more sifting through gravel.
I never vacuum my sand. Only water changes.
Fish love touching the natural sand surface. Most of natural bodies of water have sand floors. All-gravel floor doesn't exist in nature.
Tip:
Make sure you turn the filters off whenever you do any kind of cleaning/water change. The unsettled suspended sand will jam the motors!
I use play sand from Lowes. I just turned the filters off. Took the sand, dumped it into the tank scoop by scoop. Wait. Then turn the filters back on. That is all. Water clears up in 1-2 days.
Other people prefer to rinse their sand before they dump it into the tank. But I rather like my 1-2 days of haze.
