I was souly buying mine from Vine Hosue Farm until recently. Now we get it all from our local farm shop down the road much cheaper.
For a 22kg bag of wild bird seed mix it's £10 (2 bags a month)
A 22.5kg bag of sunflower heart (the birds favourite food!) it's £22 (one and a half bags a month)
Then we get peanuts, and niger seed from the market, but don't need to buy those very often. We also only put fat balls out in the winter, as the Starlings go mental and bully all the other birds when they find them.
We go through
Also be careful you don't add a new food source for the local cats.
And don't let birds become dependant on your food, especially in the winter.
I'm not sure what you mean by that last bit Puddle. Surely you're not suggesting people stop feeding the birds at any time, especially winter

It's really important that before people start feeding the birds they reaslie that as soon as the food is out they do eat it, and it will be a big part of their diet. It's not a good idea to set feeders up if you can't commit to feeding them 365 days a year.
I prefer to think of my efforts as supporting the local bird population. I can tell you that numbers have increased over the years gradually. I also think the large numbers of young we are witnessing this year are a testiment to that. I can't bare the thought of that stopping, so I always make sure there is food out for the birds. At the moment they are fed twice a day!