The idea as a whole is alright, i think. However, the whole (Xp times x) for minimum account value just wont work. There's a lot of reasons why, mainly being some type of accounts might have a lower total xp but could cost a lot more than accounts with higher total xps. Thats besides the fact that not every skill are equal in value.
The "proper" way to go about it would be to have a group of people (Staff/members) who have experience in account sales in particular, price check each account that is wanting to be sold and deducting 30% of that value as its minimum value. 30% might seem like a lot, but a lot of times some people just want to get an account sold.
However i doubt this suggestion will materialise due to it requiring multiple members with added permissions (Which probably wont happen) or members of the staff team forming that group which also wont happen since im probably the only one on there who is market-active (regarding accounts).