I have been using suet and lard for years, as fat balls and as it is. I buy the cheapest that I can find(Lidl and Aldi is cheapest at the moment) The most expensive is Tesco and Sainsburys(49p last week) Might have gone up since the snowfall!
My problem is stopping the water freezing in the bird bath, floating balls, hot water in bowls etc. have not worked. I even tried the additive sold by PRIMROSE on Amazon (pricey at £5.00p plus £5.00p P&P !!)
Luckily, the pond is still O K with the pump still working ( will have to be turned off if it gets any colder) together with an old rug on top of the pond over night.No wonder the young neighbours (with a concrete garden) think that I am a saddo!