"How to connect DC small motor to give o/p of 250-300watt...."
If you need a 250..300W motor, nohing smaller will do. There's no magical way of getting power from nowhere.
I want to make a manual robot and a person is to be sited on it
Sounds like an electric gokart to me?
so required power of motor should be at least 250Watt and the ost of these motor are very expensive in market...
Try eBay or the surplus market.
so, please suggest any other method of connecting in such away that overall power will be same by connecting small type of motor....like that.
Trying to get substantially more power from a small motor will kill it instantly. If it weren't so, there would be no need for large motors and we could drive our cars with pager motors.
IOW, you're busted (by the laws of nature)