Merchant Services through the bank can be very expensive to startup, with initial costs, fees, machines etc before you’ve even taken your first payment.
Paypal may cost slightly more on a per transaction basis but there are no setup costs and you only pay when you get paid.
Here are some useful links for setting up merchant services with PayPal.
PayPal Payments Standard Overview
HTML Variables for PayPal Payments Standard
Adding PayPal to a 3rd Party Shopping Cart
Using your PayPal Account Profile
Express Checkout Integration Guide
Testing PayPal Payments
Setup your Sandbox Test Account
Test PayPal Payments Standard Buttons