Skynexer :
We've got electric all through the field yeah. So the simplest way would be to run an Ethernet cable from the house router to (older/spare) router in the garden ? I would love the extender but it's all on a budget ha
Running an Ethernet cable would be the most direct method and probably most reliable, but also a pain. Weatherproofing of the cable would be an issue, as well as making sure it was where nobody would trip over it, break it with a shovel, etc.
It would be simpler (and probably just as cheap) to use a powerline adapter from your main router to an outlet in/near the garden, then attach an outdoor wireless access point there. There, the main issue would be making sure the outlet at the far end, where the other powerline adapter would go, is weatherproofed.
Note that this is only going to work if the house and the garden outlets are using the same circuitry. If you have a separate breaker box for the garden, for example, then powerline may not work. Then you'd be back to either direct ethernet cable or an outdoor range extender.
If the price on outdoor range extenders is a bit much, shop around. I've seen sets on sale for $60 or so sometimes. Over the distance you're talking about, you do not necessarily need a top-end system capable of covering half a mile.