For certain, Eschew feats (and other caster-specific feats) are not available when taking a Fighter bonus feat. Only feats that apply specifically to Fighters can be taken during a Fighter bonus feat level.
I'm pretty certain (90%+) that they aren't available when taking a non-caster level at a usual feat interval, but to be honest, it's been ages since I took a fighter level with my multi-classed caster.
Is this for build planning or is the character about to level? If the latter, you can just start the process and see what it gives you and cancel out before finishing. If it's the former, the safer assumption is that caster-specific feats are not available when taking a non-caster class level.
It's something I'd have to test to be 100% sure about. Perhaps someone else has more recent and/or vivid memories.
Hmm... I'm pretty sure I took fighter feats on mage levels and vice versa with Chaynce. I can't say that 100% though. Perhaps export your character to single player mod and level him or her up?
Problem with that merlin is that he would need to do that on a module that contains the custom mateirals on layo, Since Eschew materials is a layo feat, it won't show on normal character level up on Single-player or other modules, yet was a good idea.
Hmm... I'm pretty sure I took fighter feats on mage levels and vice versa with Chaynce. I can't say that 100% though. Perhaps export your character to single player mod and level him or her up?
What Lance said.
Plus, there are some feats which are designated as "General" feats and others designated as "Bonus" feats. These designations can determine when a feat is taken.
Classes like Fighter and Wizard get bonus feats every so many levels. For those bonus feat intervals, one can only select from the list of feats which are specifically designated as Fighter or Wizard bonus feats. So for example, if we assume a Fighter-Wizard multiclass, if it's a bonus Fighter feat level (every second Fighter level), the player could choose Great Cleave but not Extend Spell; if it's a bonus Wizard feat level (every fifth Wizard level) the opposite is true.
For general feat levels (every third character level), the list is usually greater as far as what one could take. Upon further thought, metamagic and Eschew feats should be freely available on general feat levels regardless of which class level is taken, assuming prerequisites are met and the Eschew feats are classified as "general" (which they appear to be). But as mentioned above, the class-specific bonus feat levels do not allow for choosing feats outside of the appropriate bonus list.