We offer both credit/debit/pre-paid card transactions through our portal as well as use of PayPal.
There's a problem with internet based payment portals. They take the bad wrap for swipe fraud. Except for phishing scams designed to simply take payment information, most credit card theft happens at places like gas stations, movie theaters or at the clearing houses in general. However most people think that most if not all credit card theft happens at web portals. With that being the case, services like PayPal do help give peace of mind.
If you were to ask me point blank how much revenue I think the company I help run would lose if we stopped accepting PayPal, I'd say at least 25%. Most of the people we service that use PayPal, do so for that very reason. At the end of the day they're still utilizing the same payment method, but PayPal as the intermediary.
I hate PayPal, but it's a necessary evil for a business like the one I run. For the OP, I think I'd make it available, but probably surcharge for it's use. Especially since he's talking about large transactions where PayPal's high fees really eat in to the margins.