what you is need 'RT feed'. There are many providers for that. Amongst the 'cheap' ones - you can google for 'market-data-provider' or just search the 'data feeds' section of this forum. If you need 'superior quality' data, try for esignal.com (not esignalindia.com) or other from the same breed.
Coming to cost, it highly varies from cheap to superior providers from 1 K to 10 K per month or more. Also, most of these providers provide data in closed binary format which may not be readable by other software. If you need the data in plain text or ASCII, then they will charge extra, and some may not even provide it. For ASCII FORMAT, you will also need very fast speed and fat pipe to transfer the voluminous data quickly - other wise there will be severe delay due to choking. So you have to consider these things to check for feasibility.