I think, the differences in prices can may be due to shashkas / looks, new model Vs old model, quality of Plastic material, etc. Internals might be the same in all the series, most important being the compressor, and all would be good enough.
In 1 TON, you may look for following:
https://ecostar.com.pk/product-category/gree-products/split-ac/inverters-split/?orderby=price&filter_btu-capacity=12000-btu
In 1.5 TON, you may look for following:
https://ecostar.com.pk/product-category/gree-products/split-ac/inverters-split/?orderby=price&filter_btu-capacity=18000-btu
These are the official sources / links from Gree, with option of home delivery, and some are available with discounts. Please check the website for more details, and if they offer delivery in your city and interested in Gree, then I propose its the best option.
Also check for installation kit and charges, and if there is some confusion regarding anything, its best to call their helpline and get all the details.
I hope, it helps. Thank you.