@beakernz
Welcome to the expat.com forum and good luck with a potential move to Bulgaria!
It's not "too good to be true", you're just coming from a very high-cost region, as Australia and New Zealand have very expensive properties. So, of course, Bulgaria is gonna look very cheap in comparison.
130-140k euros is a lot for a property (or was this for the 2?). I would suggest you shop around and look for bargains, rather than rush into it. It might even be worth renting first just to see if you like the place. It's probably a bit of a culture shock after USA/NZ/Australia. :-) For 100k+ you might be able to get an apartment in a bigger city (Plovdiv, Varna, Burgas) which would be a less seasonal rental. But Sunny Beach is the top summer resort (and Bansko for winter) so it can work too. Sofia is the capital, so that would be great too, but tough to find much under 100k these days.
But, to give you some context, I did grab a studio in Bansko earlier this year, and it was under 20k euros (furnished). Not sure such bargains are still around, but both Bansko and Sunny Beach still have some nice properties under 40k ish.
As to digital nomad-ing, Bulgaria is pretty great for this, as it has great connectivity, low taxation. and low living costs. You can do 90 in 180 visa-free with your passport. This might work fine if you travel around Europe, or if you get residence elsewhere too (Serbia and Turkey are our neighbours, both non-EU, and both easy to get residence). Having to abide by the days restriction is a bit of a pain, so, personally, I'd rather get official residence. But your call.
The fly in the ointment is that Bulgaria doesn't yet have a digital nomad visa. While many EU countries now do (e.g. Spain, Hungary). If you're already making good money this way (say 3k and up), you might prefer to get this visa elsewhere. The Bulgarian option is the D visa, and can be by investment (300k ish I believe), or commonly by TRO (Trade Representative Office) of your non-Bulgarian company. If you already have an NZ company this would be great (if it's older than 2 years). If you're self-employed (or a tax-ignoring PT) then you'd probably find it easiest to incorporate a UK company (everything can be done online), put a few quid through it, and wait 2 years (using the 90-in-180 until then).
Even as a tourist you can buy property (as long as it's an apartment without land or "common parts"). Houses with land will need to be purchased via your Bulgarian company.
There are many property agents, but I like BulgarianProperties (dot com) as it's very large and reputable with lots of listings all over Bulgaria. They specialize in expats so listings are in English and they have English-speaking agents. Even if you don't buy from them, it's a great research tool as you can see exactly what's available at what kind of price. Just FYI, when searching be aware that brand-new apartments are sold UNFINISHED as "Bulgarian Standard", so they will show up as the lowest-priced properties. Finished (but not furnished), or move-in ready (finished AND furnished) apartments will appear as substantially more expensive.
If there's a catch, it's that cheap countries have low salaries (but you can avoid this as a DN) and cheap rents. :-) And I suspect you need to be pretty vigilant about who you rent to. I also doubt that one rental is enough to live on, so you would need to really be working as a DN and bringing in money every month that way. But as a bit of extra passive income, it's great. The official minimum wage here is 400 euros a month, so I'd guess one rental will be in that ballpark. But you can't live on that (even if you live rent-free in your second apartment), and my guess is that you will probably need at least 1k-1.5k coming in (still a lot less than folks need in NZ, I'm sure).
And finally, here's a cost comparison between the 2nd cities of New Zealand (Christchurch) and Bulgaria (Plovdiv) which are of similar size. It's instructive to note that cost of living is around 50% of NZ, while cost of property is around 30% of NZ.
https://www.numbeo.com/cost-of-living/compare_cities.jsp?country1=New+Zealand&country2=Bulgaria&city1=Christchurch&city2=Plovdiv