I also did this a while ago as I had 8 drives (6x 3.5 and 2x 2.5) in a case that had 9 5.25 bays and no 3.5 bays. I looked around and settled on something from cooler master as it supported a 120mm fan and 4 5.25 drives and didn't cost an arm and a leg. Adapters allowing for twin 2.5 drives in a 3.5 bay are fairly plentiful, so it allowed for 3x 3.5 drives and a pair of 2.5's in my case. You could do 4 2.5's and 2 5.25's just as easily obviously. That extra 3.5 HDD slot is a nice feature. Others I saw only supported 3 drives, or didn't have a fan worth squat. I think there was one other in the 30-50 dollar price bracket I didn't pull the trigger on, but I can't recall the name of it.
Here's the cooler master I settled on. It requires you remove the cage to service the drives in it, but at the same time, it also has rubber grommets that isolate the entire cage from your case. Incidentally, I have two of them just sitting on the shelf now, so if you wanted one, provided I meet the post requirements to sell, I'd sell you one for dirt cheap if you wanted. It's not the sexiest looking thing on the planet though (seriously what's with the cooler master logo)?
No matter what
cage you settle on though, if you're trying to fit 2.5's in a 3.5 bay, I can't say enough good things about Icy Dock's dual 2.5 to 3.5 adapter. It's metal not plastic, and it has springs and plastic tabs on the back that allow you to simply pull the tab sideways to pop out 2.5 drives. the metal part adds to the awesome too, as while SSD's don't get hot, you're still not stacking them inside some plastic piece of junk that traps heat, and cooler is always better right?