I like to save every buck i can and last time i was here I got a 30 days unlimted AIS sim card for 250 baht. Checked Terminal 21 just to compare. It was like 850 for 30 days, yikes! So went to Fortune Town saw a True 5g sim for 15 days unlimited i believe 699! Looked for the place i went to last time and found it  on the 2nd floor there's a Lotus market and near the entrance there's a OPPO GIANT (think it says giant my pic is cut off) store that has sim cards. Think it used to be called AIS cause the coffee place pointed in that direction when i asked where AIS is. I think those might be two separate store and i went to the one on the right, i guess the "Giant" store. Think he said 2 weeks 50 baht for 10gb and 100baht for 20gb. Or you can translate the pic below to confirm. 10gb probably would have been fine but i went with 20gb. He then upselled me for the 30 days and unlimited. I thought he said it was only 50 more but guess i misheard.

It's just of Blue line phra ram 9. Fortune town, 2nd floor. I guess the store name is GIANT

TLDR

AIS
2 weeks  10 gb.     50 baht     probably would have been fine with this, will need to check my data use to see how much i use
2 weeks  20 gb.     100 baht
30 days   unlimited  250 baht  would be good if you wfh and might need data if wifi is bad at your hotel or on call when you're walking about

Maybe there's some people as cheap as me that will find this useful. Also a note to self cause i'm sure i'll forget where i got the sim on my next trip