Searches are free and you can buy GR credits to view images:
GR British Newspaper Archive search
50 credits for £5 (valid for 30 days) or 200 credits for £17.95 (valid for 90 days).
I haven't been able to find out how many GR credits it costs to view an image though which makes it difficult to compare with the deals available on the British Newspaper Archive's own site (500 credits for £6.95 valid for 2 days or 3000 credits for £29.95 valid for 30 days, 12 month sub for £79.95). On the BNA's own site images cost 5 credits (over 107 years old, black and white scan), 10 credits (over 107 years old, colour scan), or 15 credits (less than 107 years old).