I think there are several different things potentially going on here.

I can't imagine going asking a similar question in another specialized sub and getting "budget options are literal garbage!"

I don't think you'd get about the response if you went to /r/woodworking and asked about getting your data a Harbor Freight table saw, or /r/programming and said your dad was a programmer 20 years ago and gave it up to become a lawyer, what Android table should he get so he can get in the programming grove again. You came to get advice from experts and you don't like what they tell you, it sucks.

You mention that your dad is frugal. But not necessarily poor, since he has been an engineer for the last 20 years. And also that your budget is limited to around $800 because you are a college student. So it is not fair, but I couldn't help but read your note and think: what college student has $800 to drop on a birthday gift for his dad? It could be that your working full time, and paying for college and extravagant gifts out of that. Or it could be that your taking on student debt, in which case your father would be correct in saying that the gift is foolish. Or you father could be paying for your college, and your gift to him is really a case of you spending his money on something you think he wants. Now it could be that he's mentioned his lifelong passion for machining every weekend when you guys go out fishing together, but it doesn't ring true that he's not following his passion and making machining a hobby because he's too cheap to spring for a mill. Maybe he's creating art with a hacksaw and file for all we know. And why a mill, and not a lathe for example? And it just so happens that you'd like a mill as well?