We've discussed this in another older thread or two around here somewhere Alan, and it may or may not directly relate to your question. But probably relates to your main one.
<Edit to add>
I found a recent thread
on the same general subject. In a post of mine a ways down the page I link to the older post I had in mind from way back when. Both may be worth a read to give you some more ideas.
When I was first starting out with my own sites I used one of the 3rd party merchant account things. Paypal wasn't an option at the time because it required signup for anyone to pay through it. 2Checkout.com was the 3rd party service I used to be exact.
I did it because it was a really inexpensive initial fee --I think around $50 at the time though this was few years ago. There was also not going to be any additional programming fees because they offered a way to tie a link right into their own shopping cart. Now most of them also offer some type of cart you can install on your own site I think.
I knew after awhile that this choice was costing me money. Not so much in sales because of friction in the sales process, but in that 2CO charged more per transaction and a higher percentage than I was seeing being offered if I had my own merchant account.
I sent off queries to a few merchant account providers, and there weren't nearly as many then, to get the real bottom line costs if I decided to go that route. Both start-up and on-going monthly costs.
For my first site --a service site so no inventory overhead-- with my price point I came up with a figure where the monthly per transaction and percentage someelse kept vs. what I got was break-even. For my sites the figure was $3,000 in gross sales.
Once my first little site got to this level and stayed at or over it for a few months I took the plunge, figuring that the start-up costs that weren't all that much anyway were just a short-term cost of doing business and that a few months down the road I'd be ahead of the game. From there I never looked back.
Just as an FYI, my Merchant Account goes through Authorize.net. They have all sorts of scripts available you can plug right into your purchasing form if you already have something set up that works for you. No need necessarily to introduce a shopping cart into the picture. Most of these services do offer scripts or help to get you up and going.
Does this mean I don't offer Paypal as an option anymore? Of course not. I still offer it, even though a purchase through Paypal sends me a little less money per sale because of their fees.
In fact, since then I've added the ability to pay via check online with a little $80 package I bought. It basically lets them enter their checking account data (security of this data is going to be your biggest concern) which you can then use with the software to print out a draft against their account.
And I also still allow people to pay by mailing a check or money order payment.
Heck, on some of my service sites that cater to certain markets, namely schools, I even accept Purchase Orders where they get immediate access even though I know going in I'm not going be paid for a month or more.
The bottom line is you really need to sort out what works best for your potential customers. Then give them that option, or more than likely those options. In the long run it's really the only way to have a decent chance at maximizing your income while not doing any great amount of extra work.