The above link gives you your rights. Everything will depend on what your lease states. If your lease expires end of August, and you have been honoring your lease, you should have the right to stay there until the end of your lease.
It sounds like your landlord wants to work with you and give you an opportunity to buy. If you can not afford to buy the home then you could ask if he would be willing to buy you out of the remaining portion of your lease. This may help you get into another lease and allow him to get the home on the market sooner.
My advice to you is to not damage your credit by holding over beyond the end of your lease.
Have you looked into the possibility of purchasing another lower priced property?