Both species grow fairly large given good conditions. Peppered = Corydoras paleatus are probably not the greatest choice, as they are technically subtropical, and need a "cool winter" period to be really at their best.
Something like Corydoras panda or Corydoras trilineatus should be available in most places and will not grow quite so big, thus allowing for a stocking level that needs less maintenance.
There are dozens of others, but it may require a bit more effort to find those.
At 7 dollars each, you can probably find some on mail order (assuming you want more than 3-4). Although 7 dollars isn't CRAZY expensive - they are about £4-6 here. If you want "nicer" fish, then they tend to cost a little more.
I would say that if you want a smaller option, corydoras panda are the way to go. If you see julis at a store, they are probably trilineatus, and the ones I had were very sensitive. They all died of fin rot, but I currently have some bronzes in the same tank, and they are thriving.However, I may have just gotten a bad batch.
You've unfortunately been misinformed. Gravel is not suitable for Corydoras, even if it is smooth. It harbours bacteria in the voids, and leads to poor health. It also prevents the fish from indulging in their natural behaviour, digging. No serious Corydoras keeper would consider using gravel.
I would suggest that if you can't replace the gravel with sand, then it is best not to keep Corydoras, or banjo catfish for that matter.