Inukes are hard to beat for value. Most of the budget amps all have roll off around 10hz. So your 13hz would be easy to handle. But there are also DSP work arounds also for below 20hz roll off amplifiers.
It looks like the inuke 3000 is superseded and there are none around in stock here in Oz.
The Behringer NX3000 looks like it is its replacement although none of the downloads give frequency cutoff points.
OK, so I received the NX3000 plugged it in and no signal displayed. Plugged the cable into my mixer and there is signal!
Contacted the supplier and they (Behringer) said to plug the output from my mixer into the amp.