For my six string, I tend to use my digitech RP150 effects pedal to go from standard to d to b and so forth. It cost me around $150-$200 Canadian. The pedal's easy to use, and since it's an effects processor, their are many more features included like flange, reverb, chorus, distortions, etc. Unfortunately, the RP150 does not have a foot pedal.

drop A is only B-standard dropped, and I use my six string without my RP150 tuned down to play Amon Amarth songs and it's not too bad.

lol 7-strings rule!