There are many variable in the cost of siding, not the least of which is the type and quality of siding you chose. I suggest going to your nearest home improvement store to see and feel the differences in quality and to gage the difference in cost. Then seek out two or three reputable contractors to provide you with bids. The more educated you are, the less it will cost.
Siding is not usually as expensive as other options. There are many different materials available, and they all have different costs. The size of your home will also be a big factor. Make sure to get multiple quotes.
$5/square foot (installed) should get you in the ballpark. Make sure that you discuss whether the windows will be wrapped, and whether the soffit & fascia will be covered--these can add significantly to the cost.