Hello Nilo - and welcome to the Forum.
Is the Asus UX32 so old? I found the spec of the Asus UX32A which looks very good. Or are you looking for a desktop?
There are Linux-preinstalled machines available but you are right - they can be rather expensive.
If you want to build a desktop, this can be done considerably cheaper then buying ready-built and you might like to look at
https://linuxforums.org.uk/index.php?topic=13782.msg111949#new.
As for
security: 1. No computer is intrinsically secure unless you encrypt sensitive directories - which is a good idea.
2. Using a Virtual Private Network (VPN) will prevent Google/Facebook
et al tracking you. Not all VPNs (even paid-for ones) are wholly trustworth so I use
Protonvpn.com which is free and ultra secure.
Secure mail:There are very few free and guaranteed secure email services, and it depends on whether you want to use client email software such as Thunderbird (which is
very configurable) or are happy with webmail.
For
webmail, I thoroughly recommend
Protonmail.com which offers several paid-for versions and a free version of reduced functionality. The service is totally encrypted end-to-end and if you lose your password not even Protonmail can retrieve your data. Aliases are not available for the free account.
Tutanota.com also has a free, reduced-service offering that is just as secure and easy to use as Protonmail.
For use with Thunderbird
email client, I use
Runbox.com. This a paid-for service only but the cheapest (Micro) offering costs about £1/month. Again, the servers are encrypted but your data can be retrieved with a lot of hassle if you lose your password - and you will need already to have listed a second email address to your account so they can communicate with you. The Runbox Micro account allows up to 100 aliases which you should use in preference to your base address.
The service I receive from Protonmail and Runbox is excellent.
I hope that helps a bit - feel free to ask more questions.
Keith