That "request" for gas money is nothing short of of the officials tryin' to รีดเงิน "wring money" out of foreigners, no matter how you wanna play it off..
The thai immigration office thought this up, it's their deal, you're not obligated in the least to offset their home visit program.
That you buy into it, or even worse try to justify it as "the cost of living here" is sad.
I hafta ask you, "Do you find it hard living here without a spine?" If you meet the requirements to get an extension of stay why would you walk around on eggshells with some thai wearing a too-tight of uniform with a bunch of bangles hangin' off it?
I highly doubt they're gonna deny you your extension because you don't buy into the "gas money" scam. Even if they did, you could immediately file an appeal (seeing as there is now a defined appeals process for denial of extensions)..
Still you guys do what you want. I'll just be thankful that in Bangkok they don't do home visits for marriage or retirement extensions.