You could migrate the excel sheet to google sheets, which can do things automatically and is online. Since it's quite similar to excel the people at the company should not have problem maintaining it, and it can be done in less than 3 months.
However you'd have to revise the server environment and issues regarding access or even adding ...
The project I'm working on is web based price calculation
I'll only be here for 3 months and there are nobody in the office that can do any coding
Note that these two statements are already showing the main issue here: if the company for which you are working really wants to offer a web based price calculation in a permanent fashion - ...
The fact that they've asked you to do this suggests that they're at least willing to look at other ways of doing this - perhaps as a proof of concept/trial balloon.
If you design it in a modular way, the fact that nobody codes isn't an absolute barrier in itself (although it is a substantial risk given the paucity of expertise). As long as they can edit the ...