instalments

I want to buy a plot for the construction of a house. If I give the amount in one installment, I have to pay say,(1000) but if I pay in installment form then I have to pay more than the actual price, say(1500). Isn’t this Riba or this is allowed?

Kindly guide me whether purchasing the goods on installments is right or wrong? Normally, we have to pay more than the original price while taking the goods on installment and the seller terms it as “rent.” Your reply will definitely help me. Thanks in advance.