Is $500 to clean DE powder from pool a fair price?

I have a decent sized pool in my backyard. My pool filter grids ripped a few months back, shooting DE powder into the pool. I got them replaced, and the pool repair guys said the leaked DE would clean up if I ran the pump for awhile, but it never did. Last weekend, I cleaned the new grids, which were already filthy, and I've run the pump for days and added chlorine every day, but there’s still a bunch of old grey DE powder sitting throughout the pool. It's all cloudy and nasty; I can't even see to the bottom. I have a vacuum robot stuck somewhere in the deep end that I still need to fish out. I also don't get much suction from the skimmer, so I don't think I can use a hose to suck it up. I'm also only getting 5 PSI on my Hayward Filter. I don't fully understand the pump system, so I'm not even sure I have it set up correctly. The pool repair guy said it was correct with the black lever to the left, but I don't see any suction through the skimmer on this setting. I see some suction in the skimmer when I move the black lever into the middle position. I'm not sure where those pipes lead either as they go underground. I have some flocculant and will try that later today to see if it helps. The only problem is that I only have a small vacuum that looks like it was made for spas, and I'm wondering if I should rent one. I'm hoping there’s something I can do myself without paying too much, as pool companies are quoting me $500+ just to clean it. I just need to remove the DE from the bottom.