What will be the cost involved?

You can install power windows on your Maruti 800, It will cost around Rs. 5000 depending on the brand you choose, but you cannot convert to power steering as it takes lot of modifications and lot of cost and is not workable in the end.

This car is quite small with rack and pinion steering. Modifying Rack and Pinion to add power steering assist will not be easy. Since this is such a small car, steering should be already nimble enough without adding a sluggish power steering setup.

Aftermarket power window kits are available at various websites, just google ''power window kits''.

Maruti 800 is a small car in which a hydraulic power steering fitment would be very difficult & uneconomical (you will waste a lots of power to run the hydraulic pump sucking oil from the reservoir). The better option is en electric power steering (column type; just like in Alto/Wagon R) but again u will need a lots of modifications.very difficult. Both options generally cost around Rs. 25,000 in the cars where it is possible. So, not recommended.
Electric windows is a road side mechanic is job. You can get it done in the tune of Rs. 4000-5000.