I'd say look for used on the deck - It's going to make the rest of the system sound like poop. You may as well put pyle subs in... I've experienced on numerous occasions that a cheap HU will often make a system sound worse than the stock one. You will be throwing money away on nice subs if you cheap out on HU.
On the other issue, my female companion is extremely happy with just her sub and nothing done to her speakers, and I must admit it does sound decent. No idea what the stockers are like in a neon though.