I would not pay $110 for a 6x9 speaker if I were getting a sub. $110 can get you a nice set of components. I'd even use the stock speakers as mid-ranges, get some stwwters and crossovers, and a sub before I pay $110 for an axial speaker. I generally do not like triaxial speakers as the crossovers are usually not very high quality. A good 1" dome speaker can play 2500-20kHz. A good 6.5" can play 80Hz-5000Hz. Round speakers require a baffle, no cutting of sheet metal.
That Clarion 10" driver looks very nice, but I believe they are designed for use as a pair. 2-ohm stable mono amps are more expensive. Maybe try a Blueprint which would require a smaller enclosure too.
