I'd love to (do something), but (sentence)

This is a friendly, polite way to say "no" to someone's invitation:

A: Would you care to join us for drinks?

B: I'd love to, but I can't.

I'd love to stay, but I have a lot of work to do.

I don't know if (sentence)

This is a polite and roundabout way to say "no" (or "maybe not") to something:

I don't know if I'll be able to make it.

I don't know if he's the best candidate for this position.

manage (something) financially

This means to have enough money for something.

To "manage" to do something means to succeed, even though it's difficult:

I've managed to do OK.

How'd you manage to pull that off?

Your "finances" are the amount of money that you have. So managing something financially means having enough money (barely) to afford something. English speakers usually use this phrase in the negative form:

We can't manage it financially.