As a consumer who will buy online as a preference to the store, I actively avoid doing a purchase on sites where Paypal is the only method of payment. When looking at costs, do not simply compare the cost of the techncal integration, look at the cost of lost business due to a bad ecommmerce site.
POD1 - are you able to track on your website (using something like statcounter or other metrics), whether clients have initiated a purchase and then abandoned? The cost of such abandonments are the minimum cost having Paypal over a user-friendly alternative. Also you do not just lose the single transaction, but any subsequent transactions that user may have made on your site into the future.
My advice, even if it is more expensive to set up, get it right first time.