Good Bass Amp for Guitar?

To make a long story short: What's the best bass amp/amp head + cab combo for guitar? I'd prefer to keep this under $300 if possible.

Details:

I do a lot of signal-splitting, and I'm looking for an amp to meet my needs.

First, I have my guitar plugged into a y-adapter. One cable feeds into an Ibanez DE7 delay/echo, which I have set to minimum time (30 ms). The dry out feeds into my fuzz pedals, while the wet out feeds into my overdrive pedals. Sometimes I do clean + fuzz, clean + overdrive, just fuzz, or recalibrate for just overdrive).

The second cable, however, is more relevant to our discussion today.

That second cable runs from the y-adapter into a sub-octave pedal, which filters out anything higher than F on the D string, knocks everything else down an octave, and then feeds into a bass fuzz pedal. On its own, this chain creates an adequate low end; combined with the other signals, however, I get what strikes me as a full, muscular sound, and I am very happy with it. However, my amp isn't.

I'm plugging into a Line 6 Flextone II, which is an awesome guitar amp capable of delivering many killer tones. However, if I set the sub-octave signal too high, or fuzz it up too much, I can tell that it's starting to cause some damage. I don't push it too far - as soon as I notice, I dial the sub-octave down. It would be nice to have an amp that could capture that low-end without any reservations, though - something that will allow me to dial up that low end, or fuzz it up.

If the "best" bass amp for guitar is something like $2,000 and there's a good amp for my purposes for $250, I'll gladly go for the "good amp." I guess I'm really asking, what's a good bass amp for what I'm doing? Also, would it work for me to grab a guitar amp head and plug that into a certain bass cab? How might this work with a tube amp head?

If it's any help, I'm currently EQing my amp with bass at 5 of 10, mids at 8 of 10, and treble at 2 of 10.

 

I'm seeing later solid state Fender Bassman units for well under $300 - how do those fare?