[Giray]

Our company uses our helpdesk extensively. Before jumping into it, let me warn you that most sites that use tickets are very demanding. They want all the bells and whistles. If you want to develop something that is complex and that will sell for a good price, I think you'll have buyers because no high-end vb-integrated helpdesk system exists. If, on the other hand, you opt for a rather simple desk, I think you'll end up doing more support than anything else.
To give you an idea, I would pay up to USD 1000 for a great vBulletin integrated ticket system. I am talking a 'good' system.