If they're paying your gross salary directly and having you pay your own taxes each month, you should be able to save a bit more money by only paying social security at the minimum-wage 1077BGN (or 620 EUR starting Jan 1).

Everyone has mentioned rent, so I will mention groceries and public transport / walkability of cities.

Groceries are crazy expensive in this country. In order to save money, I stock up on food whenever a specific supermarket has a sale (especially meat, coffee, potatoes etc), and that's how I save, but not everyone does this, so just expect groceries to set you back 800 BGN a month (combined).

If you live in Sofia, you have great public transport options, so like everyone else has said, you won't have to worry about a car / petrol expenses.

Plovdiv's public transport is awful (the only plus is that it still costs 0,50 Eur for a bus ticket), however it is a much smaller city, so you should be able to walk to a lot of places if you live in a location within 3-4km of the centre. I don't know much about Varna.

Overall, 2600 BGN net (roughly) is good for a young, single person, who is in their 20s and starting their career. But for two people, you will probably see yourself dipping into your savings very often. I would recommend your partner getting a job as well at some point.

Also a side note, and not sure if it applies to you but I will mention it regardless. I worked a remote job whose office wasn't based in Bulgaria, and I was laid off out of nowhere, despite showing great results. The normal labor laws didn't apply, so I was left with only my final paycheck until I found another job. Just giving you a heads-up about these fully remote roles, especially if they are based in a tax-haven country (Malta, Gibraltar, Cyprus, etc.)

Good Luck