Pretty much any of the Ampeg cabs will work just fine for you - just depends on what kind of sound you like. If you like booming lows, go for the HLF's or 15's - if you want more focus and definition - go for the sealed cabs with 10's. The head will go down to 4 ohms, which is where you want to be to get the most from the amp - so you can run either (1) fridge sized cab or (2) 8 ohm stackable cabs. Whatever trips your trigger. I personally wouldn't mix 10's and 15's because they throw differently, and having all the same will be more consistent for projection. if you are looking for cheap - you can usually score good deals on Ebay or GC's used online list - but you don't have to buy new.
...but...IMHO, Avatar's bass cabinets are in line with Ashdown's, Ampeg's, Carvin's, Fender's, Peavey's, ect., ect., ect.