Is there a good basic white cotton dress shirt around $50-60? Looking to upgrade from my current $30 Macy's-brand 'slim fit' shirt, but tripling up to $90+ for Brooks Brothers et al. is hard to imagine as a PhD student. If $90 is the price point I may just go to Ratio or blank label and get them custom.

Brooks Brothers on sale—their shirts are discounted to around four for $200.

If  you only need one shirt (and you really don’t need many white dress shirts, IMO), check out the sale sections at Charles Tyrwhitt or TM Lewin.