250 watt plate amp at Parts Express was $120 shipped for me. It might be a bit more now. I paid $80 for a used Shiva. You can get the new Stryke audio 1201 which is supposed to be almost exactly the same as the Shiva for $85 pre-order right now. I built the Sonotube style cylindrical sub. Tube was $30 or so for a 5 foot piece. You can find it cheaper but it was the only local place to find it. A sheet of 3/4 MDF for the endcaps for $20. Flared port and various terminals and speaker carpet was another $40. You can use paint or cheaper cloth for finish. The hometheaterforum.com DIY section has many projects. To save more money you can always pick up a used plate amp or use an old stereo receiver and just use the sub out of your current receiver as the input to the old receiver driving the sub. So basically I built it for under $300. It's ported, looks fine to me, is pushed by 250 watts and sound great with both music and movies. Volume and port dimensions are available at the Adire audio site. I also downloaded some speaker design freeware called WinISD. It wasn't as much about the money for me (though it helped hide cost from the wife buying bits and pieces separately) as it was about making something that would be perform as well or better than anything in its price range. Plus to quote Spicoli on Fast Times at Ridgemont High, "My dad has an awesome set of tools." Actually just a router and jig saw.
Frank
