Assuming that's 8:40pm the cost difference is probably a wash for two people with the taxi being potentially cheaper. It's generally 25 euros into the city center and the train station is outside the worst of the internal traffic. If you mean 8:40am you may be in for more traffic headed into the city.
The monorail is kind of creaky but dependable at takes 8 minutes or so - the biggest factor in wait time is whether one is at the station or if you just miss it then you need to wait for it to come back.
One thing to be aware of is the fast trains in Bologna leave from 3 levels below ground and take an airplane type transfer to get to so allow at least 15 minutes extra time to get down the series of escalators and more if you want to take the elevators because they are confusing and only go one floor at a time. Unlike every other Italian train station I've been to you should never linger if you are taking a fast train. Head straight to the gate because you'll get lost at least once if you haven't done it before.
Just checking midweek dates - assuming this is pm - it looks like midweek .Italo has a 9:46pm and Trenitalia has 10:16pm. Base fare is 26-33e so you could just bite the bullet and know you'll pay that much when you show up or buy a cheaper ticket and possibly end up losing that money on a gamble. Regardless I would get the apps for both companies so you can buy tickets on the fly as you need them.
Have a great trip, Verona is lovely,
=Tod