Hi Noris, this came up a while back and I believe what others have done due to the mistake on the evisa website is uploaded the bank statement showing 20k baht for Q4 and scan a written note saying not applicable for Q10 as UJ suggested this is a mistake on the site but you can't not upload something for Q10 or the app will not go thru and the £10k is not needed for that application. Only 20k baht is.
The other option as others have stated is go visa exempt 45+30 days then extend to see wife or child for 60 which would give you the required 4 months plus a bit.
These are my 2 options when I return next month and to be honest I will probably go with the second as its a lot less hassle plus you would have to extend the original non o 90 to get over your 4 months anyway.
Good luck, maybe you could report back as to which option you went for in the end.