The highest I've gotten is wave 30, and that was with the strategy of using 5 turrets and spreading out upgrades evenly between them. Which results in me only being able to level them up once (50xp + 50g each) and being able to spend 150g on crank-action upgrade for just 2 of them before I die.
not investing in the first level up to save the 250g cumulative gold causes you to get overrun around wave 15-18 as your turrets can't even kill one thing with their abysmal fire rate, combined with being no longer capable of one-hitting red blips anymore.
All the upgrade options are there, but at the current state, the player never gets a chance to pick them up.