There have been numerous changes in the past 10-20 years which have affected the market, and have increased bat prices.
Player sponsorship values have gone up in the last 20 years. Adidas/Nike/Reebok coming into all the markets, and the internationalisation of cricket with the IPL, meant that you have to pay tens of thousands to get a good player. Adidas don't make their money selling bats, so will fork out whatever is necessary to secure the real superstars like KP and ST. Mongooses yearly sponsorship retainers were at £340,000 a year at its peak with Symonds and Hayden. It's a lot of bats you have to sell to cover those costs, but if you want to supercharge your business and get into the UK's top retailers you need to sponsor cricketers. Look how Hunts County and Fearnley have dropped off since they stopped.
Secondly - whilst the raw materials may only cost £60, someone needs to make them and there's the shipping/import taxes if that's going on in India rather than the UK. Retailers take roughly a 50% cut of any sales, so the profit margins on the majority of your bats you sell (mid grade mens, or kashmir/low grade jnr bats) can be as slim as £5-10 a bat. Retailers have also felt the squeeze of Sports Direct, and the increase in rents on the high street - that leads to them wanting discounts from the manufacturer. The internet has also changed the way manufacturers work. A manufacturer carries a lot more stock now than they did previously, as shops have a tendency to order in 1/2 bats at a time to fulfill orders rather than placing a large October and March order, like they did previously. This makes the market harder to predict, and leads to wastage.
Thirdly - It's correct in saying willow has gotten more expensive. So bat prices naturally increase. For every £5 extra you spend on willow, the end user will probably see a cost increase of £20.
Everyone is correct in saying £400 is a hell of a lot for a bat. The gross margin on these is quite good, but manufacturers do not sell tonnes of these. The majority of their sales happen in the mid-ranges, where margins are significantly tighter. If everyone was making a fortune out of cricket why would we see Woodworm and Mongoose going bust in the last 5 years? Smaller brands such as Smasher or Phoenix, have also gone to the wall. Puma have scaled back cricketing operations. Even the podfather, Julian Millichamp, has given up batmaking