You could also build a sump to your exact dimensions. I had never worked with acrylic before and just bought the pieces I need and glued it up. It was actually pretty easy. I would not want to use it as a display tank since the glue squirted out of the seems a little, but as far as a sump and holding water it looks good.
If interested, I can give you the site of a place that can sell you the acrylic for a good price. Then all you need is the glue and some glue dispensers. It does take a little time since you have to glue and wait a lot, but if you have a week, you can do it, I didn't even practice on scrap first, just read a lot and did it.
