i'm looking at new bikes and i'd really like a hybrid bike but can't afford it. if i bought a mountain bike and switched to hybrid tires, would it be okay?
i guess it would be
Not exactly since those two kinds of bikes typically take different sizes that won't physically fit on the other rims, but there is a good variety of tire widths and tread patterns available in mountain bike sizes that you could use to alter the ride/performance/handling of a mountain bike.
Be aware that there are other differences between those two kinds of bikes such as riding position, strength, weight, etc.
You can buy slicks like the Kenda Kross, use comfort bike tires, or buy 1.5 inch road tires.
usually hybrids have 700c and mt bikes have 26"
that doesn;t switch
you could just get 26" slicks though
those are actually cheap
If you mean replace your existing mtn tires, with smoother and less wide road tires - on your existing rims- YES. It would be a simple way to convert without having to potentially do some adjustments to brakes etc.