Butts about £25, b&Q
pump = £7, eBay
tank = second hand off old heating system (loads being thrown out with Combi now)
inverter = £100 ebay (more expensive as pure sine wave)
charge controller = £15, ebay (you might not need it if inverter has charge controller)
float switch = £7ish each, ebay
solar panels vary in price, but all ebay. That lot of mine are a 40w, 60w, 18w & 10w = 128w altogether.
Thinking of investing in a "grid tie inverter" to do away with the battery and sell the elec back to Manweb.