What does it mean when you say 'What I wouldn't give to be there?

Solution 1:

It's a less dramatic version of the doubtless hyperbolic

"I'd give my right arm [/hand] to be there."

(See, for example, Cambridge Dictionary)

The implication is that you'd give up many of your prized possessions / comforts in return for being there (etc).

"What [is there that] I wouldn't give [up] to be able to ...?" [implication: the list of what I wouldn't give up in exchange is small]

..................

CED actually gives the expression:

what I wouldn't give for something (also what wouldn't I give for something)

used to say that you want something very much:

What I wouldn't give for a cold drink!