The honest answer is simple:
a website upgrade costs what the work takes to plan, write, build, test and publish properly.
Random prices without context can be misleading. They often do not match the real work needed.
A small one-page website is not the same as a multi-page service website. A service business website is not the same as an online shop. A clean rebuild is not the same as fixing a messy old website with poor structure, weak text and missing technical basics.
Still, it is useful to have a rough idea.
Below is a practical guide for small Irish businesses.