For general purpose bimbling, then a rigid fork (no suspension) hybrid should cover just about all the bases.
A semi-slick commuter tyre such as a Schwalbe Road Cruiser will cope with gravel, sand and a certain amount of mud. Otherwise, as others have said, you can get a dual-purpose tyre with a slick centre and knobbly bits on the outside. Riding on tarmac on full knobblies is like riding through treacle.
And there'll be enough give in a 1.75 inch tyre that you won't need the suspension, and given the budget you're looking at, a suspension fork will be more of a hindrance than a help. So you'll have a lighter bike and won't be wasting effort by having the front end pogo-ing up and down just when you don't need it.