You probably have a lot more options than you think. There are a lot of good quality two channel amps that would have no problem running a 3 ohm load in bridged configuration. Another more stable option would be to get a class d mono that does around 1k into 2 ohms. Something like that would have no problem getting your sub moving. Those Gti's are great subs and will soak up tons of power but don't really need it to get going. I have had a 15 on as little as 150 watts and still had surprising output and great tonal quality
Just as spooney said,doesn't need a lot to get going..ran mine (15gti) on punch 150 bridged,kicker sx900.2 bridged,and finally two kicker sx650.1's strapped...plenty of options to run....
JL 1000/1 or 500/1 makes power at 4 ohm. JBL/Crown has a couple smaller amps that make good power at 2 or 4 ohm. Any of which can be had used for a fair price.