Brakes are entirely optional for MUni. I used them on my 24 MUni until I built a wider wheel that was too wide for the brake position. I took them off in favor of the wider wheel, and felt like I didn’t really need them after all. After using brakes on 24, 29 and 36 I don’t think I would put them on a 24 unless I was running short cranks (maybe 125-137 for MUni). I plan on using my HS33 on my 26" when I get around to building that wheel, but for now I have the 24 w/150’s in the 26 frame and no brake.
I would go for a ride and see what it feels like before making the investment. If in the end you still want a brake used/new Maggies from Brycer1968 will probably be the cheapest way to go without waiting for a screaming deal to show up on Ebay.
You will still need to get mounting hardware to attach them to your frame, and so you will add about $20 to the cost of the brakes.