My Middle English resources tell me the vowel is going to be like our "oo". As in "you", or "house" in Canadian. And that the "gh" is going to be like a Scottish ch, but in the back of the mouth. (It's in the front of the mouth with vowels such as e and i, in which case it sounds more like a sh.)
You can find this word listed in Middle English Dictionary (U. of Mich. Press, 1997), which you can see via Google Books. There are several citations from between 1200 and 1500. Other spellings are oughten, ohtoun, and uhhtenn, which may give you some idea of how the -ugh was pronounced. Of course, it wasn't pronounced ugg-, but perhaps with a vowel as in bout, and a velar fricative like the ch in the Scottish loch; it seems to rhyme with the Middle English past participle foughten (see below).
It sounds rather nice to me, especially in the cited phrase bothe even and oughten, meaning literally "both evening and morning" and idiomatically "at all times of the day" as in the following couplet: Thretti dayes … he had foughten With-outen rest bothe euen & oughten.