Paypal is dead easy to setup - just login to your account, got to "Profile" - "My selling tools" and click on "Create new button".
Go through the options & set it up but leave the amount to be paid blank - this will let your customer type in how much they owe.
You can use the "let your customer leave you a message" option for a "First line of your address & daytime contact number" line, making it easier to keep track of who's paid.
Once you're finished paypal will generate some code for you - just copy it & past it into your website & its done!
GoCardless is a much better option though in the long run as it puts you in control, and the transaction fees are a lot less.