That's exactly it.  I'm barely making anything on these as it is, almost nothing, really.  I do it pretty much to help people who can't find stuff locally.  If I upgraded my account, I'd have to raise prices.  Heck, as it is I'm tempted to drop PayPal altogether, but then almost no one would order.  As it is right now, I get very few orders.
If PayPal would only charge for credit card transactions, I might do it, but when you upgrade you are hit for *every* transaction.  If the orders were larger, I also might consider it, but on a transaction of say...six dollars, they take about a buck.  A buck on $20 or even $30 isn't bad, but a buck on a $6.00 transaction (which is average for me) wipes me out.
But hey, if you guys want me to raise prices...   

If you have a checking account, you can always do an eCheck thru PayPal.  That doesn't require an upgrade, but it does take a few days to clear.