Charging for a service

My suggestion is to charge hourly, if it isn't going to last an hour break it up in 15 or 30 minute chunks of time round to the nearest half hour or hour. Then charge for development, testing, release, and post release testing.

If you have any experience with this CMS, it is probably not such a big deal.

But from your question it seems you have not worked with Wordpress before. And if you are new to WP you will have a learning curve. (This goes for any CMS.)

I only know Drupal, however I will share my experience nonetheless: If you know how, it will take anything between a few hours and a day if everything goes well and the client gives you all the info and codes. If there are issues, and there always are, it might consume quite some time. If you are really stuck it might take a few days. And don't forget your client will need after sales service, in the form of support. In all candor: I would ask for something like 300-400 dollars, nothing below that. Including warranty and excellent service of course, as long as the site is not updated or worked on (read: sabotaged and utterly destroyed) by someone else who works on the cheap. Just my 2 cents.

Let us know your experiences.

This could be accomplished by adding a few plugins in 15 minutes or less - or could be much more. So you need to define Twitter & Facebook integration.

Does this mean adding social sharing to posts? Custom social buttons that link to their social profiles in a footer or sidebar? New graphics in custom colors to match their site? Twitter feeds added to a footer or sidebar? Facebook Like box? First, quantify exactly what "twitter and facebook integration" means to your client so you can quote an accurate price.