My wallet has grown to over 350 million as the last of the four Onyx cruisers sold, and 50 of the 100 Invulnerability fields have moved as well. With another 90 million in those mods still to go and 40 X-Large Shield Booster IIs coming out of the factory tonight (retailing for another 80 million ISK or thereabouts) I should be over half a billion very soon.
I got another 20 BPCs for invention of Invulnerability to try, and I have more tech II ships I should build. In about a month is not out of the realm of possibility to have built back up to a billion ISK again. Of course, this can only lead to another shopping spree, either for a good PvP Rokh or maybe get that Widow I've been eyeing up.
Time will tell.