I'd say treat it as if they were about 4th level characters or so for an XP budget.
I based that guess on taking the total HP for a group of 4 CR 6-7 monsters (160 hp x 4 = 640), then dividing it by 3 (est. how long a combat is supposed to last on average), then dividing it by 8 (number of "average" encounters during a day). That gave me 26 - so I checked to see what CR monster does around that damage per round - which is CR 3). Then gave them a bump for being PCs in this case (and having access to HD for healing). What that basically tells me is supposedly how long they'd last before an adventuring day wipes them out.