$86 for a tranny fluid replacement and filter change isn't a bad deal at all. I think that's pretty good actually. $400 for an axle is nuts, but the axle by itself is $328.89 from
SubaruParts.com, part #28021PA061 (Item 03,) so maybe it's not that steep after all.
Any auto parts store should have an axle for considerably less, maybe $150 or so. These are almost always a rebuilt unit. Generally, they replace the whole axle. Each axle, or "half-shaft,' consists of an inner constant-velocity [CV]joint, a shaft, and an outer CV joint which also is the hub spindle. It's possible to replace just one joint, but this is rarely done for some reason. (It's actually quite easy to do.) Normally a complete, rebuilt half-shaft is fairly inexpensive, so it's probably just not cost-effective for a repair shop to rebuild them, and thus the parts are not offered.
Did you get taken for a ride? Well, not if their cost on the part is anywhere near the $328.89 you or I would have to pay. Usually their cost is less, but that's part of their profit margin and probably not unreasonable in this case. You'd have to find out what their cost is to find out if you've been had.