One of the advantages of getting a well-known sofa type is that you can often get cheaper re-upholstery and cushions as they don’t need a fresh measure every time and can make them up in bulk and post them through.
We bought an old second hand ercol daybed frame for £300ish, and were able to get new cushions, with good quality removeable fabric covers for about £350 from these guys:
They sell overstock on ebay too, for a bit less than we paid, but we didn’t like any of the colours they had on there at the time.
Add a bit of elbow grease restoring the frame and re-webbing it, and we had a ‘new’ sofa for about half what you’d pay for a restored one, and a third of what you’d pay for a new one.