How much does it hurt to cut yourself with a blade from an exacto knife?

Not much. In fact cutting yourself doesn’t hurt much at all, and I say this as a result of first-hand experience. I’ve used exacto knives, razor blades, hunting/utility knives, kitchen knives, scissors (good hollow ground hair scissors) and both western and Japanese style straight razors. The actual cut is barely noticeable unless the edge is dull or you go very deep and cut a nerve, or cut yourself somewhere very sensitive like the sole of your foot or palm of your hand. It will sting afterwards, but this is not that noticeable although if you cut yourself enough it will eventually get properly painful.
Hunting knives hurt the most as the blade widens at a steeper angle from the edge, and leaves wider cuts that not only sting more, but will be more prone to scarring. Japanese razors have similar properties and although they don’t widen as much, or as steeply they’re much sharper and can cut far deeper. Straight razors or disposable razor blades cause the least pain, but the most bleeding.
Exacto-style knives are neither especially painful, nor especially good at causing bleeding. They’re usually fairly dull in contrast to the other edges I’ve mentioned, and while this can make them painful it has more to do with bruising than cutting. If you sharpen them yourself they perform like an extra-chubby, duller version of a razor blade.

Wanbasion Black Stainless Steel Knife Set, Sharp Kitchen Knife

It’s not too bad. It depends on where you cut yourself. I cut my self on the thumb with an exacto knife while making a model. the knife went the entire width into my thumb, so I just went and washed it off, then put a bandaid on it, then put medical tape over it to stop it from bleeding. Thank god exacto knives aren’t serrated.

Smith & Wesson Extreme Ops SWA24S 7.1in S.S. Folding Knife with 3.1in