Visiting Oxford from Brackley I have found the following do reasonable priced meals. Browns in the Covered market University Club just down from Kings Arms in Holywell st, then left. Wok and Roll , Woodstock Rd reasonable priced chinese and the chinese eat there as well. By the castle there is a eat as much as you want just of the Wetherspoons Swan and Castle. Far from the Madding Crowd friars entry between Gloucester Green and magdelan street prices £7- 9 .
I like Wetherspoons (the menu and price) but don't go too often because we haven't had one very close by (I live in Abingdon) BUT we now will be having our own branch opening up in the old post office in the High Street, so if anyone's travelling out this way, it's worth bearing in mind.