What volume of elution buffer for plasmid-containing filter paper?
The answer to this is... some.
You only need a tiny amount of plasmid DNA to transform bacteria like DH5$\alpha$, typically in the 1-10 ng range, but much less, as low as about 10 pg (10 picograms) may still work. If you can get even 0.2 ul of the liquid out of that tube, try using that in the transformation.
Things you can try;

remove the paper, spin the tube down and see if you can recover even a tiny amount of liquid.
Add a bit more liquid - another 30 ul will be fine
Snap the tube lid closed on the paper to hold it in place, then spin the liquid out of the paper - this is quite difficult to do.

Note - even with 10% DNA recovery (very low for this method), with 30 ul you will still have 100 ng of DNA, or about 3.3 ng/ul.