It occurred to me that Ty may be building you a 4 ohm loudspeaker. If the dual 10" midwoofers are run in parallel, then it will likely be a 4 ohm (or below) load. In that case, 99 dB efficient at 4 ohms is equivalent to 96 dB efficient at 8 ohms. An 8 wpc 300B SET amp may not be enough in this situation.
For something cheaper than $500, you might consider a Dynaco ST70 (lots of them on the market, lots of tweaks/mods).
For something cheaper than $500, you might consider a Dynaco ST70 (lots of them on the market, lots of tweaks/mods).