With this in mind, I've worked on a piece I call 'the 10 minute field'. Basically, its a simple terrain piece that takes about ten minutes of your time to make (if we ignore the time required for drying out, that is!).
Start with a square piece of card or foamboard. Apply a coating of universal filler (the white stuff that comes in tubes to fill cracks in plaster and the like), flatten it out until it covers the base then simply draw lines in it - closely spaced and parallel (and obviously to scale with the figures you use). My example is for 6mm but can easily be adapted to 15mm and 28mm scale.
The base with universal filler, the lines drawn in it and the 'blank' around the outside.
This is a 3" square piece for 6mm Napoleonics
Leave a 'blank' space around the lines (which represent a ploughed field) - this is for some talus and flock to frame the cultivated land.
Then allow to dry (I put mine on the radiator). Then apply some PVA glue around the blank space and apply a fine talus.
When dry, paint the whole of the piece dark brown - ensuring that that paint gets into the bottom of the furrows. When dry, you can either (as I did) apply a dark brown ink into the furrows (to create a better contrast) or just leave them - then lightly drybrush the remainder using a light brown then cream paint.
The piece painted brown with inked furrows for contrast
Once dry, simply apply some grass flock to parts of the talus and you're done.
All told - about 10 minutes actual work for a usable terrain piece.
With talus added and drybrushed
The finished article - with 6mm Prussian artillery for scale
I've seen similar stuff on the market for £5. I'd estimate that in the cost of materials, the above piece costs about 20p to make - a bit of a difference.
If you want, you can then take on a greater challenge (such as using painted pan scourer or chunky talus embedded in the universal filler) to create a field enclosed by hedge or wall).
Or you can really go to town and flock the ploughed area to represent the crop growing.
Good luck!