My home policy (Zurich) is £500 per unnamed bike, but happy to take named ones, so the three that are worth more than that are named. They do new for old on anything they cover.
You can quibble with insurance companies, you don't have to agree to their offer. You'll need good evidence that it's worth more (receipts, photo's, etc. help you might even find historic posts on here are a good trail if you kept a build diary). You may find that they argue second hand parts aren't worth as much, but again you should always be able to fall back on the argument that they need to be able to replace what you had so if the parts are that cheap they should be able to find them. Get your own quotes for a sensible replacement, don't trust them to do all the work, and wave the ombudsman in front of their noses if they mess about. You're talking small amounts of money to them so providing you're not trying to get more than they'd ever offer (saying 'yes' to that would worry them) at some point your chasing them is going to be costing them more money in time and aggro than just agreeing.