As I recall (it’s been a couple of years since I used PayPal) PayPal will automatically send the auto responder to the person who made the payment and also to the designated email(s) for the account.  There is a test area (sandbox) you can use to test your website.  The Thank You webpage must be done by the webmaster.

@beckyflansburg

The thank you page should be developed by the web people/agency you are dealing with and shouldn’t cost any extra.

Good luck!

@beckyflansburg For sending regular automated email from your website (after registering or after sign-up) then its a simple matter of scripting something probably in PHP. 

For sending automated emails from PayPal after a donation, purchase, etc – then PayPal has the tools to do this.

Hope that helps.-Rob