Thule aero bars should be able to accommodate pretty much any roofbox, they are a little wider than normal bars but my standard Kamei box fittings work fine with my Thule aero bars.
Look at other makers of boxes than Thule, they attract a silly premium price. After a LOT of research I bought an ex display Kamei delphin roofbox from roofbox.co.uk for a lot less than i would have had to pay for a second hand Thule box. Might be worth your while looking at things other than 2nd hand.
Also worth checking BMW, VW, Ford etc etc as they seem to regularly have sales of their own branded roof boxes at massive reductions, some of these are manufactured by Thule for them.