Can I find good sub woofers for cheap?

Hi, about 9 years ago I bought two 10 inch subs for my car that are made by Advent. Not a popular brand, I gave $35 each brand new. These things have been through 4 cars, and I just replaced the amp (also 9 years old) with one that makes more power then the subs are rated for, so I keep the gains down...anyway my point is that these speakers sound freaking good !! I play them loud everyday and after 9 years they will still piss off the neighbors. My question is...does anyone know if there is a woofer out there that I can find for cheap (around 50 bucks each), and still make some real nice sound. I can't remember where I got the Advents at or if they are even in business still, or I would look for some like what I've got. The only reason I would like to replace these is the larger (newer) amp I just got. Thanks in advance.