Bitmain BTC miners comparison

Hi Guys, im looking for some better understanding regarding the Bitmain BTC miners and hope someone here can help me, looking at the website i can see that for exemple 2 models (T19 Hydro and S19 Hydro) are marked at an extremely low price, compared to (S19 XP Hyd and the S19 Pro+Hyd) marked at 19890 and 15k, why all this difference in price? how old are the S19 and T19 Hydro model? i do see a difference in T and a better efficiency for the last 2 models

Thanks in advance