Don't be fooled by expensive branded panels, they are not worth the premium that you pay for the slightly decreased degradation and sometimes shorter warranty, I spent many, many hours doing research, as I designed my own solar system inc. battery storage, there are many great panels for not huge sums of cash e.g. the Jinko 395w (JKM395N-6RL3-B) are ~£140, and have a good warranty and are a very well respected brand in the solar industry. As for inverters, if you are going for a battery backup, then you can look at Hybrid ones, as they act as charge controller and inverter for your solar. I said in the other thread, sourcing my own kit means I spent a lot less, and still have a really good sized system (6.2kW solar and 8.2kWh battery), installation costs will vary depending on who you can get to do it though.