Shakespeare is public domain and you can essentially do what you want with it in terms of modernizing or adapting.  Dover thrift editions are $1.50 / script and the editors state :  "Performance - This Dover Thrift Edition may be used in its entirety, in adaptation or in any other way for theatrical productions, professional and amatuer, in the United States, without fee, permission, or acknowledgment. "    I don't love the editing of this edition, but they are very useable, and if you do your homework you should be good to go.  The scripts for Midsummer, Much Ado, and Two Gentlemen (among others, I'm sure), lend themselves very well to temporal adaptation.  I've seen Much Ado set in WW2 and the Civil war.  And I saw a wonderful Two Gentlemen set in the old west.  50's and 80's are fun times to use too.  We changed Midsummer to be taking place at "The Athens", a ritzy golf club instead Athens, Greece.  The Mechanicals are caddies, the Fairies punk/Goth...it's been a lot of fun!  And we've made almost no changes in the actual dialogue.  One or two small cuts, but traditional language.