Probably way different then what you are thinking and in a small town. But I opened a small ice cream store in Michigan last year...
http://forums.pelicanparts.com/off-topic-discussions/469868-anyone-own-ice-cream-parlor-4.html
I figured a budget and doubled it. Still wasn't quite enough. Again probably way less then what you are thinking too. But if your space is already set up as a restaurant that'll save some money remodeling. Also ask yourself why didn't they make it. Location?
Also, for me I haven't quit my job so I have to have people working it while I'm not there. Honestly, labor costs are killing me because the volume hasn't picked up yet because we are new and the word is spreading around. It'll get there as summer approaches here...
Lastly, it was a lot of work and pain in the butt to get open with inspections, etc, and you are never really 'off' of work. But it was also very rewarding and exciting to take the plunge. My only serious recommendation is not to borrow/spend more then you can pay back or, if you have a family, affect them too much.. For me, it would have been much harder if my 6 & 4yo had to give up there activities and the wife gave up some of her stuff to make it happen.