Can modernbill integrate to 2CO? How?
And can it have recurring function? how?

Yes, its already built into it

No, but I think they are working on it.

I got an old version of modernbill. How do I integrate it to 2CO? I cant see 2CO in payment option when logging into Admin

The module is integrated into MB, it's under system config.

If its not there then your version does not have it.

I think its only $29, or something like that to get 6 months support which gives you access to the current version, and any future version for the 6 months.

Its well worth it IMO

got to pay it again?!, it is ridiculous....... they should give it free