So when I set out to fit some aftermarket seats to my 1989 BMW 325i, I decided to make my own brackets. The level of complexity can vary depending on whether or not you want to add adjustable slider brackets, etc..
My seats didn't have sliders, so I decided to add some aftermarket slider brackets, which upped the complexity, but I'll just go over the basic idea here.
-1/4" x 1-1/4" mild steel bar stock (~5-10' depending on your setup)
-measuring tools (you could get by with just a measuring tape, but something like a caliper comes in handy as well)
-metal working tools (bandsaw, chop saw, angle grinder, drill press, etc)
I built my brackets at the TechShop, in Menlo park, where they have all the tools and equipment I needed, but if all you have is a hacksaw and a cordless drill you could probably do everything but the welding. If you want more info about TechShop, check out their website, www.TechShop.ws