Are (any of) the special materials in the CRB always available?

[NielsenE]

Unlike the PFS guide, the SFS guide doesn't call out availability of any of the CRB's special materials. However making a weapon out of a special material doesn't raise its item level, so perhaps its implied that its allowed, but that seems open to lots of per-table GM interpretation.

[Gary Bush]

There are only three; Adamantine Alloy, Cold Iron, and Silver. I would say the Special Materials listed on page 191 are always available within the confines of their use detailed in CRB.

There is no limit on how much a character can spend on an item other than what the character has available. The limitation is what level of item can be purchased.