There is currently ~$2.46m of USDC in the DAO wallet (wallet.ensdao.eth).
Assuming the DAO can get more than $13m from the auction (10,000*1,300), this would leave the DAO with ~$15.4m in USDC. The minimum bid for this auction is set at $1,300/ETH.
The main USDC expense comes from ENS Labs. ENS Labs receives a daily stream of $11,500 USDC, which amounts to ~$4.2m per year. Over two years, that is ~$8.4m.
The other main source of USDC spending comes from working groups. Working Group spending is not fixed, can be lowered, and often carries forward from one term to the next. This budget would allow working groups to claim up to ~$1.5m in USDC per term between them. This amounts to ~$3m per year and ~$6m over two years.
With these numbers, spending for 24 months would amount to ~$14.4m in USDC.
Assuming we can get an average ETH sell price of $1,300, this would leave the DAO with ~$1m at the end of 24 months if no additional ETH auctions/ sales are conducted.
The ENS Foundation will likely also request annual funds to cover expenses. These expenses are outlined here and amount to ~$42k per year.