Blueberry Oatmeal Pale

I'm making myself a hopped up oatmeal pale ale for Christmas drinking. I was thinking about adding blueberries but at about a quid for 100g in some places I'm thinking it's not worth it. I have 400g in the freezer but I'm thinking this won't be anywhere near enough for a 23L batch. What do you think? If I was adding fruit what is the best way to sanitize them?

I used 4.7 kg of blueberries in 20 litres of wheat beer (see here) and the flavour is very subtle so 400g won't come close I'm afraid. Better to use a fruit with a stronger flavour, I'm thinking of maybe a raspberry porter next.