tbh i wouldn't be expecting too much out of it...
2m for a +7 muffler and ~4m for dragon tail
put in a reduction multiplier (around 0.7) for it being slotted and i guess you could expect 3-5m.
Personally i would say that slotted ancient capes or undershirt or sov woulda been better, but this is pretty ok for those with a limited budget - so again don't expect the people who would buy it to be able or willing to pay too much...