I don't often see a good 16v sx for sale less than $6000, this means one that doesn't blow smoke or crunch gears and has a desent interior/exterior. You're talking ae92 sx right ?
I think that $7100 isn't that bad if you're 20 valve conversion was done well and everything is fine with it.
I myself have an ae92 sx seca 20v and would like to think it's probably worth $6000 - $7000, it's in pretty good nic, not perfect though. Keeping this in mind i've seen ae82 seca/hatches with 20valves selling for 6/7 or even moreo, but they're usually covered in pearl or have big silly chrome wheels etc.
Catcha,
Seeks.
PS hope this helped you in some way deciding on a price.