Suggestions for AutoTuba Amplifier

I recently built the AutoTuba by billfitzmaurice for automotive application(of course) and I have been having trouble finding a suitable amplifier for it.

What I'm looking for
100watts RMS into 4 ohms. Variable LP filter(the higher order the better, but anything greater than 12db/octave will suffice) and perhaps a subsonic filter @20hz or so....

The most important thing is that it will do 100watts RMS into 4 ohms... and I'm looking for something cheap <$80.

Any suggestions are greatly appreciated

Thanks guys
I like the Alpine V12 amps. 30w x2 will do bridged at least 75 watts and its clean. Find a used one on ebay or something.

I am interested in the autotuba; can you give more details. I won't be able to build one in my single cab taco, but I would like to know how it works out for you for future reference.
The autotuba is an 8" hornloaded design. Billfitzmaurice came up with it and plans are available for $9.95 US at his website

The horn increases efficiency by acoustically coupling the driver to the surrounding air. On average it runs 10db hotter than a sealed enclosure(according to bill's measurements).

It only has somewhere around 100watts RMS power handling which makes it an easy add on for a car stereo requiring no modification of the electrical system

Come on guys... even pyramid sells cheap amps with variable filters on them..... I said 12db/octave would suffice but PREFERRABLY better.... I just wanted to find something that could be Bridged into 100watts RMS or is Mono into 100watts RMS.... I didnt want to have to buy a 2 channel amp and only use one channel. I can find a 2 channel that will do the trick for that cheap, but I'd rather not have a channel that is being used for nothing....

Any ideas, suggestions just let me know