NI is one of the few raw food suppliers that doesn't have a massive minimum order, I think it is 5kg. The food comes in 1kg plastic tubs, so 5kg wouldn't actually take up a huge amount of freezer space. Although obviously it works out much cheaper to get as much as possible for the same delivery charge.
They are a great company, very knowledgeable and with top notch customer service.
Pre-made is definitely the easiest way to get into raw, my Mum feeds both her dogs (elderly JRT and rescue Whippet) and her cats on NI.
I haven't used them myself but check out Honey's and Wolf Tucker as well, same sort of thing, they might have a supplier nearer to you.