I think wordpress for the backend would be best for you. It allows all the things listed in your project including easy to use admin area. There is an adsense plugin available and the google adsense code goes into widgets, pages, and posts very well. This would be the quickest way to build the site which will keep the project cost down. For the paypal, I would just need you to build the button in your paypal account and then send me the code to add to the page. (Paypal now creates encoded secure code for buttons so account information can not be seen and I choose not to have banking account logins from my clients. If you have not created on of their buttons before, I think you'll find paypals step by step is very easy to follow.)