Need to know how thick of a sand bed you want, but you can always start with 150lbs and then add more if you need to. Most of the sand your going to find is in 50lb bags. Remember that sand being a smaller diameter doesn't take up as much space as gravel would.
i always use less than 1lb per gallon i used 100 lbs in my 125 and it looks great,50 lbs in my 75 and both have a nice layer,sand spreads better than gravel so you can get away with less.but in the end its up to your individual taste.
I dont want it to think. 100 lbs sounds good to me. So I have a gravel vaccum that hooks up to my sink how do you clean sand with out sucking it up? Also is there a place that sell sand for a good price they want $30 for 25lb bag of sand at my LFS not sure if thats a good price.