DIY is the way. You can customize it to you whatever specs you want.
Although I have made a DIY W/D out of a 20G high myself for my hopefully freaking soon 125 g (waiting on delivery..slow turds) I made it where the bio media will hold approx. 7gal of bio balls. Also put on top of the tank/sump a plastic 2 drawer tray that is about 3 inches tall each drawer. These will hold (top) filter pads and the bottom any other media, planning to put 1 liter of Azoo bio glass, 3 chemi-pure, and if need be some CC to help buffer the water down the line.
Now that comes out to about 8 gal of bio media, which should be more than enough for a 125 g. Going to use 2 mag 7 pumps, one for each return, since the 125g AGA has dual megaflows built in. You can never have enough filtration.
The possibilities with a DIY is endless, and its cheaper in the long run to build it...plus the big factor is, a sense of satisfaction from building it yourself.
With the 50 you plan to use, you'd can do so much with that baby.
Get some egg crate plastic, its pretty cheap from HD, a 2x4 sheet, if you want some acrylic sheets and either cut them to size or get the biggest sheet you can afford and cut it yourself, some aquarium safe silicone and some of your spare time ...then you're good to go.
Don't forget to get some ball valves, so you can adjust everything while testing it out.
1" ball valves are about 7-8 bucks at HD, and 3/4" around 5-6 bucks.