I think you and your fiance are in hybrid bike territory - hybrid bikes will give you an upright position, a frame that's a bit beefier than a delicate road bike, and appropriate tires for both pavement and gravel. You may be able to get away with a cruiser, but I'd personally recommend something with multiple gears if you are going to ride on gravel.
An entry-level hybrid from a local bike shop will probably run $400-$500 (per bike). The value in the higher price is that they're likely to do a tuneup after you have some miles in (to make sure everything is running properly) as well as a free annual tuneup. This can be helpful if you do not know about bike mechanics or have the tools to do your own work.
Not all department store bikes are complete garbage, and there are some that are reasonably decent at a lower price point (say, $200-$400) from places like Target, Dick's, etc. If you go that route, look for a sturdy frame, avoid features like shocks (which are likely to be horrible in that price range), and have the bike inspected by a shop for assembly issues. These bikes are likely to be a bit heavier and have lower-end components that are harder to keep working properly, though it might not be an issue for low-mileage riding.
Good luck with your bicycling journey!