A hidden, highly popular all-you-can-eat street food buffet operates near Lumphini Park, offering roughly 12-15 varied Thai dishes (curries, stir-fries, rice) for only 50-55 Thai Baht (approx. $1.50 USD).
The stall is situated just outside the perimeter of Lumphini Park, often frequented by locals and workers near the MRT stations. This local spot is renowned for its extreme value, welcoming atmosphere, and authentic, freshly cooked food.    Location: https://www.google.com/maps/place/เฉลิมชัยข้าวแกงบุฟเฟ่ต์+50+บาท/@13.734126,100.5444028,15z/data=!4m6!3m5!1s0x30e29f906439472b:0x25e72988f7bf9e11!8m2!3d13.7316155!4d100.537793!16s%2Fg%2F11h_bv0ft_?entry=ttu&g_ep=EgoyMDI2MDIxMS4wIKXMDSoASAFQAw%3D%3D   Video:

LOCUSTS -  That is exactly what Hong Kong city people name the  tourist/ stayer from main land China, no ill intended just description of fact.

Like a plague of locusts!....platters of prawns and duck are blitzed in seconds!!

The biggest threat to the public at Bangkok buffets are Chinese tourists who don't dish food on to their plates, but grab entire platters directly from the serving line to take back to their tables.   

I haven't tried it but as a rule I'd avoid buffets (especially at lower prices) in tourist places like that. There's always better food nearby in Bangkok and I tend not to trust buffets like that for hygiene either. Obviously, if you really wanna to go to the observation deck and are hungry it might have uses but it's not something I'd recommend to my friends who visit Bangkok.