>You can have icloud disabled?
Settings > iCloud > Sign Out
You can also skip iCloud sign in altogether during the initial device setup.
Also, if you do choose to sign in to iCloud, you have full control over which iCloud services are enabled:
iCloud Drive, Photos, Mail, Contacts, Calendars, Reminders, Safari, Notes, News, Wallet, Backup, Keychain, and Find My iPhone can all be enabled or disabled individually.
And, if you enable iCloud Drive to share files between your Apple devices (kind of like Dropbox), you have on/off control over which apps (if any) you want to grant access to your iCloud Drive.
>Doesn't iMessage still phone home though?
Settings > Messages > iMessage > off
>Doesn't apple cease to support the latest iOS versions for older models, creating potential security risks for those who retain them?
Apple is really good about supporting their hardware, much more so than Android, and especially with security updates. the iPhone 4S (released in October 2011) runs the latest iOS release (iOS 9.3.3, released a few days ago)
>Also, what to do about the exorbitant costs?
an iOS device is a good investment. longer software support means you'll save on the cost of having to upgrade your phone's hardware more frequently (unless you want to, of course).
the iPhone SE is a good lower-cost introductory device that should last years. just be aware that the new flagship iOS devices usually get announced in September, so it might pay to wait it out for a few months to see what gets released.
(Apple rarely if at all cuts prices, so to maximize the value you get from what you spend, it's worth it to buy in at the start of a new device's lifecycle.)