We calculated the cost according to this formula: 

15p per inch perimeter of outer frame + 3p per square inch for the glass + 20 p for each butterfly.

 The final size of an A5 size picture is approximately 6.5" x 9" which makes the cost 

(15 x 31) pence for inner and outer frame + (3 x 6.5 x 9) pence for 2mm clear glass + (20 x 8) pence for the butterflies 
which makes a total of £4.65p + £1.75 + £1.60 which makes a total of £8.00. Variations from this price would be because of the type of frame chosen but we have several types of frame at 15 pence per inch.

ways to contact me are: 

e-mail:   ad@derricutt.force9.net 
telephone: (with answer machine if I'm not in) 020-8904 9112 
address: 70 Barnhill Road, Wembley Park, Wembley, Middx. HA9 9DE 

I look forward to hearing from you!