You may simply pick the additional spell Gabbro gains at Level 2, although you can't cast it until you've had time to rest and memorise it.
Wow! That's so generous! Thank you sincerely! I was prepared to just memorize Sleep a second time until I had 1000 GP to research a new spell. Now I'll have to think about which spell to take...which is a lovely "problem" to have!
I think the 1,000 GP/level cost is only to rewrite/recover a lost spell book, or to research a brand new spell. So, I'm only waiving the requirement to find a mentor and spend a week studying.
No other class has similar requirements upon levelling up, so it seems a bit harsh on arcane magic users.