Cheaper ways to heat a log cabin workshop (UK)

Hello good and clever people of Tildes, I need some advice.

With electricity the price it is, and my wife having a sizable workshop in the garden, I'm looking for ways to bring down the heating cost.

Her workshop is 5m x 4m x 2.2m, and the wood is 44cm thick. It's a chunky beast. She makes gifts and personalised items, so when she has the heatpresses and mug/tumbler press on the go, it gets toasty. If the sun comes out, also toasty. However, over night, it gets super chilled, almost to whatever temp is outside. To combat this I decided to use a Govee Electric Space Heater, 1500W with Thermostat, WiFi & Bluetooth. However, this barely does anything and the electric usage flies up.

What are good options here? The office is about 10 metres from my house. It's too far to extend the home central heating via plumbing, plus too much lagging. I don't want to spend a fortune, so any sensible options I'm willing to entertain. If we're talking a couple of thousand, it's off the menu.

Thanks for any help.

Dropping an edit with a link to the actual cabin: https://www.tigersheds.com/product/the-gamma-44mm-log-cabin/

It's not like a USA style log cabin, that's for sure!

Edit 2: Okay - wall insulation looks like the next thing to tackle before even thinking about heating it. Thanks folks.