180, you could get an acrylic or glass aquarium (or any food grade water resevoir) and modify it to become a sump... It's not to difficult, depending on what you would like to do?
I know someone who was setting up his large tank with a 55 gallon acrylic tank as a sump. He picked up the tank used. The price was even reasonable, if I remember correctly. If the tank or soon to be sump has a few scratches it really isn't a big deal.
Do you have pictures of your limitted space that the sump is going into, so we can help?
What are you planning on putting in your sump? skimmer, and etc...
What ever sump you get/build I think it is a good idea for it to accomodate any and all water from the tank when the tank is turned off or the power goes out. Here is a sump volume calculator for you to play around with:http://reefcentral.com/calc/sump.php
Have fun!