In my experience the e-visa is better to avoid any delays at the airport. You can get an approval within 24-48 hours before travelling, however, it is better to get your evisa 7 to 10 days before your travel.

Do they both cost the same?

There’s not much difference.

535 SAR is the e-visa and 660 SAR on arrival.

I have observed that the visa waiver option is not advertised well (likely deliberately, as it's cheaper!), plus, the online form is only available on MOFA, where you have to fill a longer form than you would if you were applying for an e-Visa.

 For us, as a family of 12 people coming from USA and UK, it's a no-brainer that we are applying for Visa Waiver and would save around SAR 2950!!

 One may argue that e-visa and Visa on arrival are valid for multiple entries for one year.

 My reply to this is that you only save money on the visa fee using these two options if you intend to visit Saudi more than 2 times in a 12-month period.

 So my advice to UK passport holders is to consider using Visa Waiver rather than an E-visa or Visa-on-arrival.

The visa waiver is at least 2 times cheaper. The downside is that it is a single entry only and valid for 180 days from the issue date.

 You can use this website - https://visa.mofa.gov.sa/

All of the opens are good, but at the same time it is worth being aware that you could be denied taking zam zam water back with you, as zam zam is only allowed if you have an umrah visa.

If money is not a big issue, then I will go for eVISA. It covers you for medical emergencies unless you have your own health insurance.

If you are planning to travel 2/3 times in a year, then it’s worth it.

The Saudi Arabia Electronic Visa Waiver (EVW) is a single-entry travel document that allows UK nationals to visit Saudi Arabia for up to 180 days. It can be used for business, tourism Including Umrah, educational, or medical purposes.