Bottom line is: You don't need expensive monitors. But it makes life a lot easier.

Think about it: You need to make your music also sound good on the crappy speakers everybody has at home anyways.. Your music needs to sound good on crappy PAs at party, on crappy earplugs, on crappy car stereos, crappy PC-speakers and of course crappy home stereos...

So why should you need some high end speakers?

Obviously all the mentioned systems above sound different. What you have to do when mixing is to meet an average which sounds good on all systems.

The good thing with High End Speakers is that they try to provide you with a linear sound or you could also say "average" sound ..

The trick is that having a range of different speakers available to listen to, this will provide you with that average sound too. Maybe get a couple of used ones from old HiFi's and connect them to your gear so that you can switch between different speakers while working and listen how it sounds on some cheap shit speakers. If you can make your music sound good on all those speakers you did the job without any high end speakers.

there is a little catch to it... your room.. it will "fingerprint" all speakers in it. So no matter if they are high end speakers or not, the reflections of the walls are characteristic for your room and will influence the sound of all speakers... especially Bass. In any case you also need to listen to your music in other environments.

Over time you will get used to the sound of your room.. you will know what problems it has.. maybe it swallows bass, maybe it emphases it.. usually it does both on different frequenies... so you will know how to make the bass in your room so that it sounds good everywhere.

Basically it all comes down to knowing your room and your speakers. You can theoretically live with one pair of medium speakers. You can produce professionally if you simply know how you have to make the music sound on your speakers in your room so that it sounds good anywhere. If you have better monitors there simply is less to learn. Thats all.