rea·son·able
a : being in accordance with reason <a reasonable theory> b : not extreme or excessive <reasonable requests> c : moderate, fair <a reasonable chance> <a reasonable price> d : "inexpensive"
with that said you can get the factory sealed guide strait from Victor Ireland for about 130$ shipped with his autograph (If and when he lists it)
as for the OP I don't think Working Designs made the Sega CD guides so they were not made in the same limited quantity as the games so they are neither rare or expensive.