Something I have been thinking about but haven't looked into..
How much in transactions every month would be needed for a merchant account to be worth it instead of going through paypal and 2CheckOut?

Well it would depend on where you merchant account is and what your gateway would cost you monthly plus the other fees. I have a merchant account and handle visa, mastercard, discover, americanexpress plus travelrs checks, etc... my gateway is quite reasonable as are the processing fees that only one transaction a month off sets it and keeps in in the black actually

You also have to remember if people are paying through paypal, they are probably doing it because they didn't want to use another processor, like 2CheckOut.
If they didn't want to do that, they may not want to use the merchant account either, so you might just want to count up the transactions through 2CO only.

Approximately $1000. Give or take.

If you're routinely paying $40-$50 in 3rd party processor fees each month...that's about the break-even point for how much - minimum - you'd be paying through a merchant gateway (like Authorize.net). So you'd need to look into things like how many transactions are being processed a month, et cetera ad nauseum.

People should start seriously researching merchant gateway providers and / or secure server setup solutions when they start averaging $800 a month in transactions. That's getting close to the point where they may want to make preparations to shift over (if they don't already have some ideas of which way[s] they want to jump).

(Individual business patterns vary more than stripes on different zebras, so analyze your own traffic / sales / billing trends rather than just using an arbitrary number.)