I agree, just stating that within his budget he is limiting that a bit.
Currently they appear to be on sale for $570, something having to do with backorders I think.
Yes it's supposed to be a good sub but as I understand it the less expensive PB12-NSD is probably going to give you more output. It's bigger though, the SB-12 falls towards the smaller side so you're paying extra to get what it offers in a compact size, but it doesn't have as much output as other subs.
DIY is definitely a good route to go, but if you're not sure you want to jump in to that all the way there are some sub kits you can get that seem to be pretty good deals and require a lot less manual effort and skill.