In my area, I have seen them for 400-450 lately.
L025 has been mentioned, but some other larger cactus are L024, L600. Some of the smaller ones are L114, LDA105/Typhoon, L096/L160/Spiny monster.
Any royals would be cool if you can find a bigger one. My 11" royal has zero care about my 11" oscar even when she decides she needs to attack it(it doesnt end well for oscar).
One that I highly recommend with your mix is an L014(and their cousins: L368, L253).
Not sure how you plan on doing things, but you have to be careful with some of the meaty plecos and small ghost knifes. My L114 when it was only about 3.5" killed a small ~3" ghost. I think it wandered into his cave at night... found it swimming erratically in the morning with 2 obvious fang marks in its head