Re-key or just replace deadbolts?
It massively depends on the quality of the locks. I buy Home Depot cheapies, and I just replace locksets using the package codes on the lock-sets to get multiples of the same key.  (If you have 3 sets that all say "Key Code 12589”, they will all have the same key). 

However I am transitioning to using Schlage Primus, a dual-keyway patented system which precludes unauthorized duplication, and warrants top-shelf hardware.  

Go find the kind of locksmith who has a bricks-and-mortar presence with a showroom (and isn't all outbound).  Bring in a lock you want re-keyed, with the key that works in it, and the key you want to work in it.  Come up to their counter.  They will tell you whether it's worth re-keying.  

By that I mean there are 3 kinds of locksmiths: 


Virtual locksmiths, who only exist on Google, and harvest the identities of people who need locksmiths, so they can "generate leads" (sell you as a sales lead to a locksmith), or engage in criminal behavior toward you, such as casing your home whilst getting a copy of your key. 
Truck locksmiths, whose business is a van, and who mainly do emergency work.  They only do outbound work, always charge a hefty service call fee, and have gotcha pricing on everything else.
Showroom locksmiths, who do outbound but also have a retail premises you can visit with a halfway respectable showroom. They will do amazing stuff for you very cheaply.