Just want a phone that doesn't lag between process switching and can take decent photos while lasting an entire day of normal use. I feel like spending for a flagship phone is outrageous for this use, surely something more affordable can be had?

You would need plenty of RAM and a big battery ; take a look at Acer 630S

Sent from my SM-J700F using Tapatalk

Just bought a Lenovo K3 Note for 5200THB from Lazada.

That should fit the bill!

I've given up on buying a new smartphone for the minute, relying on the trusty ole mobilephone instead.

Thought there was a good recommendation with the Motorola Moto E (for less than 100 USD), it turns out it has lagging issues, mic/speaker issues, no flash and camera is awful. (previously I thought could live without a decent camera on the phone, but need a camera at least 8MP I reckon for decent pics)

If anyone can recommend the same as the Moto E (2nd Gen) without the above issues, I am all ears.

The Asus Zenphone-2 models have sufficient RAM and run very smoothly,,,many variations to choose from.

The Lenovo K-3 mentioned previously has had great reviews.

If you are willing to shop online and wait a bit, The Xiaomi, Meizu, and LeTV brands (among others) sell very powerful and well made phones for under $200