Abdul Azeez
Think Wayne Brooks response was dead on. Learn how to estimate costs yourself, at least to a point where you're comfortable closing or pay someone. Build in a buffer for your estimate. The worst you are at estimating, the bigger the buffer needs to be.
It is less likely someone is going to offer their services for free in terms of the time to do a walk through and cost estimate unless there's some incentive for them.
You've locked up the house and it's during the inspection period, it's much more likely you'll actually own the place as opposed to a house you're merely bidding on.
You get a referral like you did from your realtor and you're borrowing his or her social equity with that contractor, then I can see the contractor doing a one off.
You have a pre-existing developed relationship with someone, that person might be willing to go the extra mile if you use that benefit sparingly. So go network.
There are a bunch of other scenarios where someone might walk through without the charge (call 20 guys and someone may bite for a free walk through and cost estimate), but it's up to you to develop that scenario and it's unlikely to be the random contractor called off of the internet.
Good luck