Should I pay off and what are the fees associate with selling in the future

[Jef A.]

I am at a point where I can pay off about 200K on a mortgage for a property that is worth 500k. I am struggling with the idea of whether or not I should pay off the property and then buy something else and slowly pay that off. I have already paid off another house and rent it out and that felt good so I wanted to do the same thing with the townhouse I am in. 

Also what are the fees associated with selling a house...I suspect the real estate agent gets 6-8% (which is ALOT in my opinion). What other fees would I have to deal with to sell the property? Is there a tax for the sale of the property? 500k sale price minus agent fee of 30-40k is a lot to me so I am wondering what other fee is on top of that....is their another tax I have to worry about?