I would agree at that price point a home built sub would be a viable way to go. I have an existing subwoofer, a 12" DVC subwoofer from parts express and a BASH 300 plate. These came in well under $300 total, I bought a sheet of MDF for the cabinet for about $30. IMHO this unit blows away any thing you hear from the big box stores.To calculate the cabinet size you will neet to use one of the several speaker designers on the internet. I use Box Plot, you enter the speaker parameters, and it gives you a recommended box size along with port diameter and length. If you want your MDF cut to specification, another option is to contact a local cabinet maker. For a price they would be willing to make the proper cuts and they would be much more accurate than the local sales person at the big box hardware store. Another option is to purchase a hand held 'skill saw', and use a straight edge for making the cuts. That way you can 'measure once and cut twice', as I often do. I am currently in the process of making a 15" sub for my 2 channel system. Would any one in the forum be interested in a play by play with pics of the build?