If a customer wants something n a particular budget and you know very well it is not possible but the customer insists on the same. How to explain?

In any stressful situation like this, the best approach is to lay it all out on the table. this will surely test your patience and self-control. By laying it all out on the table. I mean, show him all the figures one-by-one...material cost per piece and how many to use, labor cost per hour and how long it should be done, etcetera. That way, your customer will clearly see the picture and will realize your point.

To be able to manage and handle this situation, I'm gonna explain and give option  that there are  items that fits customer budget and showcase to the customer all the products, But then, if customer insists that he/she really like that same item, I will let customer know that if you can wait in discount sale period maybe the same item will be included, i will immediately inform him/her..But again, if the customer can not wait the discount sales period, I will explain that this price can not be change because it the price range of the item in the market that the customer wants and after all the item that customer wanted to buy is good quality and the customer will not feel any regrets after buying the item that the customer really wants and I will advise him that you can come back in the store any moment when you have enough budget in gracious and polite manner...And I will tell the customer also, that I will keep in touch with him/her whenever we have new arrivals item to have a customer relationship that will stay longer to not feel him/her that I am not underestimating his/her ability to purchase an item and also for keeping the image of the company in delivering customer service as a good will.