You’re looking for a good service for a price that you find acceptable, OK. That’s very understandable and “legitimate” by any and all standards.
But what does “legitimate” really mean when instead of asking the perfectly obvious question “is there a cheaper service provider?” you ask a question that translates into “was i deceived?” or “was i cheated?”. Were you? Is there anything strange, unethical, or illegal about a certain service costing more in one place than in another one? Did the notary office that charged you NT$1800 deceive you about the fee? Or did they perhaps deliver an inferior product or otherwise cheat you? Or did they perform the service you needed to your satisfacton? Why does it seem legitimate that the service provider you dealt with should deserve your contempt just because you were not sufficiently informed about the larger market situation?
If you define the fact that different translators and notaries are openly advertising and charging different fees for a certain service as “rip off”, then it seems perfectly fair to me to define any translation service that costs more than what Google charges (zero) as “ripping off” its customers. After all, you only paid 2.4 times what someone else said they paid (information that has not been substantiated yet) while both of you paid infinite times the amount that Google charges.
Anyway, compared to the project you are working on that all is really an insignificant matter - it was just a sideways comment, related to some minor irritation at that moment…
There is no reason to believe that rates for translation and notarization should be anything in particular - they are what they are (perhaps in this case in a range from NT$750 to NT$1800, or, if you include Google, from NT$0 to NT$1800 ).
Your search for the lowest possible rate is fine with me, as i said (and why should it not be?). That does not mean that you were ripped off…