i think that you should maybe think about doing it yourself, its not that hard to do, maybe some quiche and carrot, celery and cucumber stix with dip, you can buy those 4 tray dips, coleslaw and potato salad, you can get that in huge tubs from the supermarket.
I wouldnt worry about sarnies, do french stick and let them butter them themselves and do finger food, chicken or veggie nuggets, little bhajis and prawn ring, you can get those in iceland for a about a fiver, it might mean the cooker but beleive me you can cater for lots of people for next to nothing!