Replacement screens and costs

You're correct, if nothing else has to be fixed, the price for a screen replacement done by Apple or an Apple Authorized Service Provider would be this:

Screen repair service pricing

Repair and replacement costs depend on your iPhone model and your AppleCare product coverage. Apple will run a diagnostic test to determine whether your iPhone has experienced additional damage. If it has, or if it needs other repairs, you may need to pay an out-of-warranty service fee. Accidental damage isn't covered under the Apple One Year Limited Warranty.

Model	Screen repair cost
iPhone 6	$109
iPhone 6s, iPhone 6 Plus, iPhone 5s, iPhone 5c, iPhone 5	$129
iPhone 6s Plus	$149

Plus a $6.95 shipping fee, if required. Fees are in USD and exclude local tax. Pricing is for service through Apple. The final service fee we charge will be determined during testing. Pricing and terms vary for service through an Apple Authorized Service Provider.

copied from: Service Answer Center - iPhone /USA

Apple will only replace the whole unit if the damage goes beyond that and/or this damage can't be fixed, for example water damage, phone got bent, etc.

Out-of-warranty repair service

If your repair isn’t covered by Apple’s One Year Limited Warranty, AppleCare+, or AppleCare Protection Plan, your iPhone might be eligible for out-of-warranty service. For example, liquid damage isn’t covered by warranty but might be eligible for out-of-warranty service. Some damage isn’t eligible at all, for example if your device has been broken into multiple pieces. See Apple’s Repair Terms and Conditions for complete details.
Read Apple’s Repair Terms and Conditions

Model	Out-of-warranty service fee	Battery service*
iPhone 6s Plus, iPhone 6 Plus	$329	$79 *available only if battery fails Apple’s diagnostic test
iPhone 6s, iPhone 6	$299
iPhone 5s, iPhone 5c, iPhone 5	$269
iPhone 4s	$199
iPhone 4, iPhone 3GS, iPhone 3G	$149

Plus a $6.95 shipping fee, if required. Fees are in USD and exclude local tax. Pricing is for service through Apple. The final service fee we charge will be determined during testing and may be less than the service fee listed above. Pricing and terms vary for service through an Apple Authorized Service Provider.

Out-of-warranty pricing varies for Apple accessories such as adapters and Apple iPhone cases. Contact your carrier, Apple, or an Apple Authorized Service Provider for more information.

copied from: Service Answer Center - iPhone /USA

Here's the Service Answer Center - iPhone page for Australia. Has this been an Apple Authorized Service Provider?

1. iPhone Screen RepairRepair and replacement costs depend on your iPhone model and your AppleCare product coverage. Apple will run a diagnostic test to determine whether your iPhone has experienced additional damage. If it has, or if it needs other repairs, you may need to pay an out-of-warranty service fee. Accidental damage isn't covered under the Apple One Year Limited Warranty.

   Model	Screen repair service fee
   iPhone 6	A$ 188.95
   iPhone 6s, iPhone 6 Plus, iPhone 5s, iPhone 5c, iPhone 5	A$ 218.95
   iPhone 6s Plus	A$ 248.95

   The screen repair service fee includes a A$ 19.95 shipping fee. All fees are in Australian dollars and include GST. Pricing may vary for screen repair service through an Apple Authorized Service Provider or your wireless carrier.
2. Out-of-Warranty ServiceIf you own an iPhone that is ineligible for warranty service but is eligible for out-of-warranty (OOW) service, Apple will service your iPhone for the out-of-warranty service fee listed below.

   Model	Out-of-warranty service
   iPhone 6s Plus, iPhone 6 Plus	A$ 518.95
   iPhone 6s, iPhone 6	A$ 468.95
   iPhone 5s, iPhone 5c, iPhone 5	A$ 428.95
   iPhone 4s	A$ 308.95
   iPhone 4	A$ 248.95

   The out-of-warranty service fee includes a A$ 19.95 shipping fee, which applies only if service is arranged through Apple and requires shipping. All fees are in Australian dollars and include GST. iPhone out-of-warranty service may also be available from an Apple Authorised Service Provider or your wireless carrier. Pricing and terms may vary.When setting up out-of-warranty service, Apple will request credit card pre-authorisation for the maximum service fee listed above. This amount will be deducted from your credit limit. The final service fee we charge will be determined during testing and may be less than the service fee listed above.Certain damage is ineligible for out-of-warranty service, including catastrophic damage, such as the device separating into multiple pieces, and inoperability caused by unauthorised modifications. However, an iPhone that has failed due to contact with liquid may be eligible for out-of-warranty service.Apple reserves the right to determine whether or not your iPhone is eligible for out-of-warranty service.