Assuming you were not BH'ing in any way or breaking eBay's TOS. I can see a few things that will work in your favor.
THEN I started getting threats from the other sellers saying if I didn't increase my prices they would close me down.
Two things here:
1. Their demands that you raise prices as not to undercut them is paramount to
Price Fixing, and that is Illegal in the US and most of Europe as well.
2. The fact that they threatened you brings in the
coercion part, also illegal almost everywhere in the world.
Certain categories on ebay are controlled by select groups of sellers. You found one of them. If they are powersellers they call their reps, also they continuous report your auctions. Enough reports (with their shill accounts) and you will get banned.
I doesn't matter how big the 5 players in that particular niche are. If they tried to coerce you into setting prices to their benefit and eBay lets them get away with it; eBay as a corporation will be an accessory to
Price Fixing and you can take them to court ~not just for your unpaid earnings, but for damages~ Let alone the fact that if what you claim happened turns out to be proven true and documented in civil courts, eBay would also be criminally liable.
I say gather all your evidence and send it to whatever the highest point of contact you can get within eBay and PayPal. Don't just call the customer support line and talk to the person that picks up... Ask for a supervisor and if you get one, ask for someone even higher up in the food-chain. If they give you the runaround, just let them know that you are prepared to take civil action... You'll see how quickly they change their tune.
As for your desire for revenge towards the other sellers... If you provide eBay with proper evidence that they did what you claim they did, I would be willing to bet money that their accounts will get shut down. I doubt eBay would risk any possible liability just to protect a handful of power-sellers.