Based on my research, I went to TAP Plastics and purchased OP3 acrylic ($16.75 / sqft).
It is much clearer, and more known than what Michaels was trying to sell me for the same price called "Conservation Acrylic". There is a way to get them to bundle a custom frame and the not-so-clear acrylic for $42, but it is of the same unknown brand.
I can return the glass I bought from Hobby Lobby and they will install the new acrylic for free.
As for the overall best conservation on a budget with already rolled posters, here is what I am doing: (Yes I know it would be better at a custom framer but I am on a budget) (Price is for 18x24)
$16.99 black MDF frames premade from either Hobby Lobby, Michaels, or Amazon.
(Wait for either 50% off, 70% off, or buy one get two free) The frames aren't amazing but they look pretty nice, are cheap, and are good enough. Everyone says don't get MDF, but they have been fine so far. Michael’s frames are higher quality than Hobby Lobby imo. They also come with glass, not that we care, and usable mounting brackets if you wanted to be super cheap and save $3 buy buying the wire yourself. (You’d have to wire a lot of frames to make it worthwhile tho) However, they have horrible staples that are a pain to take out. There is an image comparison below, I’m not sure there’s a huge difference but given the choice I’m choosing Michael’s.
$12 Lineco Frame Sealing Tape to prevent any lignins in the MDF from leaching into my art. You don't need a whole roll per frame, just a few cents worth. I got it from Amazon, local stores are significantly more expensive. Hobby Lobby will seal it for you for free if you use them to buy the foam backing. Not sure about Michaels.
$50.25 OP3 (UV) Acrylic from TAP. It's currently $16.75 / sqft or you can get anti-glare for just a little more. I didn't get anti-glare as I don't like how it makes the colors seem dull, scratches easier, costs just a little more, and if it does scratch, you can't buff it without removing the glare coating. Glass was my first choice but glass doesn't allow the print to breathe which can cause it to stick or to mold, it is heavier, and it can shatter potentially ruining the art. Matteing would be better to keep the poster off the glazing material, but I want exact-size frames and the concert posters generally have to be rolled when you're at the concert to prevent immediate damage.
$6 acid-free foam backing. It's not Japanese cotton, so it may still contain some lignins but it should be very good.
$3 mounting from Hobby Lobby: points, screws, paper backing, and mounting wire.
Hobby Lobby might tell you that backing paper won't stick to the MDF paint but it will, if you push back they are likely to just paper it for you anyway. If they don't, you can buy some online. If they do and it doesn't stick, Elmer's glue. yes, it's not great but it is so far away from the art that it will be fine.
The total cost for my frames is around $77.50 each and should preserve and display my art for years to come.
Some other notes: working with an independent shop is great, but they won't be nearly as forgiving if you change your mind and will likely cost a little bit more than a chain store. That being said, if going with a truly custom frame, they will definitely be able to help you way better than the big box stores.
The Queen poster (red, front) is Hobby Lobby and the Metallica poster (colorful, back) is Michaels.
