Not fair.
I use Arista Premium too, because I love Tri-X, and it's inexpensive, so to me it makes no sense to pay 40-50% more for the same film in a different box.
But if you like TMax, then you should buy TMax, regardless of cost. Compared to the time and effort you put into making your photographs, from exposure to finished print, the cost of film is insignificant even if it was $10/roll.
+1. The cost of film is fairly negligible overall, compared to all other costs to photography and print making. But for some, especially students, their budget may be quite tight, and then Arista Premium is very attractive. I try to use the best film I can afford, so that afterwards if there is a special negative, I don't have regrets about the medium it was captured on. And of course it has to do with one's visualisation of how one would want the print to look etc. But I also believe if a picture is worth taking, it is better to capture it on any film, rather than none.
I have used Acros fairly extensively, and develop in Rodinal 1:50 with gentle and infrequent agitation. It gives fine grain and does a bit of highlight compensation. One does have to watch the highlights with Acros. TMax 100 may be the better film for you if that is a worry. I am not sure what you mean when you say the midtones are flat. It can be the particular lighting conditions, or maybe the way you develop. Aren't you over-agitating? That is one of the main issues when a negative looks flat, and it causes other types of problems too. Flatness mostly lies in micro-contrast and not in the overall tone curve. It is that which makes eyes look dull and foliage not to sparkle etc., and it is very sensitive to agitation with some developers and dilutions. I wouldn't know what applies in your case without more data. My Acros negatives look and print fine, and they do not look dull to me. Acros is about the only film where I have virtually no worries about grain in 35 mm. I also use FP4+ and HP5+, and TriX and TMax400, from time to time. But in all those cases I accept some grain as trade-off for speed, or I like the look of the film, in spite (or maybe because) of grain. Shooting HP5+ or TriX in 35mm makes the grain very obvious, depending on how it is developed, and it can give a nice effect on the smaller negative that would be lost with MF.
Rodinal and HC-110 are very similar, and are "honest" grain developers, i.e. they show the grain as it is. Fine-grain developers in many cases can be destructive of very fine detail, but one would have to have the lenses and technique that resolve those details to begin with to worry about it. It is an often discussed topic, how to get the least grain for a given film or developer, or combination of the two. So there are a few ideas around. The smaller the format, the more reason to pay attention to it. To the best of my knowledge, high temperatures are not good, and one should try to develop as cool as possible. With Rodinal, developing at 16 - 18 °C might even be preferred. 25 °C would not be recommended. I would think the same applies to HC-110, and possibly to other non-solvent developers as well.