Think of a Tandem!
Ok, it may not appeal to everyone, but shared exercise can be more fun than 2 single bikes, and it doesn't have to be expensive either.
We have hod ours for nearly 4 years, and do regular local rides around West Sussex, both rural, and (luckily) along the coastal paths, all for an initial outlay of £400.
We have cycled to Guernsey, fully laden with 4 panniers, and had a magnificent time as a short break, and because we are not 'died-in-the-wool' racing types, a gentle ride of 20 miles is very easily accomplished. Other than the Guernsey trip, where we piled on the daily miles to 60+, we can easily get a 30-40 mile ride local to us.
Our bike, a Viking Saratoga, ( brought used, and had done a LeJog by the previous owners) whilst maybe not having the 'top dollar' equipment, does us proud, and we really enjoy being together on the same bike. It's a real head turner too!
If you're thinking of getting a pair of singles, factor in a tandem, because it's so much more fun!
I'm considering a write up of the specs of our bike, and a little bit about our trips - if you need any advice, drop me a pm!