No there's not any limit for cash sales in GST but per don't accept more than 2L cash against per transaction or per invoice or from one person otherwise its violation of sec 269ST of income tax act 1961
In GST there is no limit but as per Rule 46, if the value exceeding 50k , the name & address of recepient is be mention on bill And As per Income tax , as replied by Mr. Mayur , i agree with his reply