If its single entry eg 90 days which is what you're talking about you need to show £1000 for 1 month (multiple entry 1 year is 10k for 3 months). On the items they ask you for something that's applicable for the multi entry like the 10k just upload a page stating "NOT NEEDED or NOT APPLICABLE" as it won't let you continue unless you upload something.
As mentioned by someone else the evisa site caters for many different types of non o. If you need further clarification you can email them directly at
*************************
but this information I gave above was from an email they sent me because I needed exact details for a non o parent of Thai child but the single entry 90 day visa financials are as above.