As others have said, web wallets are not the ideal solution for those looking to store large amounts of crypto.
I am of the opinion that web wallets are not the ideal solution for anyone, ever. Even if you want to store a small amount of crypto which you can access from anywhere in the world, then almost everyone has a phone which can run a mobile wallet, which is magnitudes more secure than a web wallet. If you don't, then I would still rather carry a paper wallet which I could import when I needed to use it rather than rely on a web wallet. In the very rare scenario where you need to cross a border and worry about being searched or having your electronics seized, then I would rather memorize a seed phrase (which would of course still be backed up on paper) than the log in details to a web wallet.
Otherwise I don't think there is any threshold for how much bitcoin you own before you buy one of these hardware wallets.
I agree. A Nano S or Trezor One are only about $60 each, and both companies regularly offer discount codes or promotions to bring the price down further. Even if there is no promotion ongoing, if you head to either of their subreddits and ask for a referral code, you can usually get a discount code of between 10% and 25% from a helpful user.