1. There is already a thread that fits your needs:
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2. The Black Market is for trading and NOT for answering questions like this.
3. What do you mean by saying "lvl 90 char with gear" ? It depends on it's
quality obviously, which you gave no indication of. My farm character also has "gear", but no gear with any notable value.
If your character has high end gear and has a few rare mounts and/or titles I would propably deem the value at 40€. If it's just a mediocre level 90 character I would say 15-20€.