What are you planning to mine (what algorithms)? What is your goal? How many and what type of GPUs? How big is your space?
I am not a big fan of low cost self made rigs, that saves you money when you start but in a long term will turn out to be inefficient. Give us some more input data, then this conversation will be more productive.
I am planning to start 6 gpu how much will be the possible cost of 6 gpu ?
What people are telling you is what you are asking is like asking how much a car costs. I could buy a 1994 beater for 500.00 that runs and gets me from point A to B or a 2018 Ferrari.
A GPU rig is a computer with multiple video cards. Go on Newegg or ebay and price the parts you want to use. You could use new or used parts. You could mine with 1050TIs or 1080TIs. Hundreds of dollars difference.
You need a mining motherboard, a power supply, a processor, memory, hard drive, risers, (monitor, mouse, keyboard, way to mount the mining motherboard), then you need which ever GPU you chose to use.
You also need to know how to put it together.
From there you need to get it running and stable. GPU mining is more of a hobby rather than money maker. We GPU mine just because we like it. If someone new wanted to get into crypto and mining I would
NOT recommend building a rig knowing nothing.
Currently, I can buy a ASIC miner for less than a video card on ebay. I could then just mine and use the coins earned to purchase the coins I wanted or reinvest into new gear (ASIC or GPU).
You can buy a D3 or L3 for 200.00 on ebay with the power supply. All you would have to do is plug it in, set it up, and you are mining. It takes hours to get a GPU rig up and stable. There is also a large cost with GPU mining vs. small cost for ASIC currently.
Just a few things to consider.....