most model only print one size, i.e. 6x4, the cost per print (ink and paper) is about 30p.
You can use commericial printing house such as Jessops for 10p if you print 50 in one go. Some on-line sevices are very easy to use. You can modify your photos and email off for printing out and get the results back in a few days.
If you want big size, you can get printing house to do it and use a good quality A4 printer to do it.