Another way to get currency.

Theres many ways to get around the market. If you want my tip is to mine and get good pickaxes and good mining then ill give you my second tip.
MCMMO WILL HELP.

Providing a new currency similar too survival rock is not possible without disabling another building block. The reason they use Bedrock is because it is impossible to obtain bedrock in vanilla minecraft without spawning. There are no other blocks of its class left to use as currency so it is not possible to make a second currency.

To reassure you of why survival rock is balanced as it is:

The idea of Survival Rock is that if you grind hard enough you will be able to find many of them, which makes it a sufficient source of income by the philosophy of- "You get out what you put in"

False, what is so hard about grinding Survival Rocks? Nothing. I could easily afk a mob farm/spawner and make a stack of survival rocks within near minutes. I've made about 6400k every five to ten minutes shoot I've made 300k+ within two hours.

Twister has a point I myself find mining another great source of income although it may not be the best or fastest and the grind of making money may be a giant pain but you'll feel accomplished once you get max rank. On the other hand if you get max rank just camping mob spawners then well there's no happiness in that.

I personally get my money by mob grinding at my skeleton spawner. It's a great wat to get $$$ fast bro! Hope this was helpful in any way