I have never been disappointed by Orion subs starting with my first set of 12" XTR DVCs back around 1990. The new XTR and XTR-Pro are solid values. I've seen some great deals on the HiFonics HZ series too and they sound very good for an inexpensive sub. Right now I've been using quite a few MA Audio and Audiobahn subs for myself and friends with excellent success and you can find excellent deals on them right now if you shop around.
Our local shop is always a great source for inexpensive carry over models too. JBL, Memphis Audio, Cadence etc. stuff can always be had for under $90 each in a pinch.
To be honest, there is so much of this stuff around that if you go with a known contender [JL/Orion/MA/Infinity/HiFonics/etc] and stay away from the pretenders [Kicker/Pioneer/Crunch/etc], you'll be fine. Also, if you stick to the more mainstream companies, at least you won't have to worry about them going out of business next week...
that's my version of reality....