Along T2 between Porte de Versailles and La Defence

I always stay in this area and have nights out.

In Porte de Versailles, you can find many budget hotels or apartments. Along the T2 on the Porte de Versailles side, such as Les Moulineaux and Meudon sur Seine, there are some decent resonably proced hotels as well.

From Manchester to Paris, I think you can check the low-cost Ryanair.

It not a good idea to take EuroStar because it's very expensive. I take it for business trip only and take the advantage of buying cheap wines in Gare du Nord :) However, if you have enough time, Eurolines is a very good coach service, but you vitually lose one day comparing to flight.

Paris is very safe with many night-out places.

Three or four days may be too short for sightseeing whole Paris. You'd better Google "Paris sightseeing" to find it out. However, having said that, I'm sure you'll visit Paris many times in your life. Any day will be a good day.

Bon Voyage