Since you are based in the US, you have more opportunities available. I would suggest checking out Paysystems if you need a third party processor.
However, you are constantly billing over $1,000 a month, consider a merchant account.
You have a few different to choose from, but your discount rate should be around 2.25%-2.35%. Also check to see if they consider hosting a high risk account - which means they might require either a deposit or a rolling reserve. If they do - keep checking. There are other processors out there whose underwriting bank do not require as such.
Understand as well that if you do get your own merchant account, you are looking for bother a payment gateway & a CC processor. You cannot have one without the other. The gateway connects you to a specific platform to verify the CC data. There is also usually a cost involved - $.30-$.35 per transaction when accessing the gateway.