How Realistic is $500 A Month?

You had spent ~2 years on this market and made 226 models, check how your sales go for that period and do the math.
If you hope that some magic will change things for the better, that's highly unlikely.
There will be more competition, quality requirements will go higher, new software will come up and models will become outdated.
To keep the level you have to make new ones.
Check your stats, extrapolate and decide if you think that it's worth the time you invest.

First of all, you will never achieve it by selling your models for $2 or $3.

To be very honest, with over 200 models in your profile and based on the obvious quality of your products, you should be very close to that goal already. If not, then it may be time to reevaluate a few things. Of course, you can always just keep grinding away and making new products, etc. However, sometimes you can be really hurting yourself by pricing items far lower than what is necessary to make a sale, resulting in payments that seem underwhelming.

True story: When I started out, I used to believe that lower prices mean a higher volume of sales, so I used to sell some models for $2 or so when I started out. Yes, I was making sales on those products, but my income was still very low. Sometimes I did not meet the minimum monthly payout, despite having sold dozens of models that month. As I continued to add new models to my portfolio, more sales would come in on certain models, but still, my income was frustratingly low.

So with nothing to lose, I reluctantly decided to change the price of my models from a minimum $2 to $5, just to see if it would impact sales. To my relief, it did not affect my average sales at all. So, I decided later to increase my prices again to $10 minimum. Again, I did not see a noticeable decrease in volume, but I did see a dramatic INcrease in profits for the month. My payouts were now almost 4 times what they were before.

So ultimately it occurred to me that I was really shooting myself in the foot when it came to my own potential earnings and from that point on I decided to really pay much closer attention to what I was charging for the models. As a result, my income became much more sustainable.

By the time you create enough models (by the current market standards) to earn 500 a month, the market will deflate (sellers saturation) even more, you won't win the race.
You can rely on it as fun for paying some beers, definitely not a reliable growing business.

The world is full of people who get rich with the most unusual things, they all have one thing in common, they work tirelessly on their own.
The 3D model market hardly exists in itself, since there are a thousand ways to obtain a model, but there are all kinds of untapped niches where a good designer can find gold, yes, at the cost of an intense and sustained effort , just like any other human activity.
I would never have imagined a spaghetti sandwich, but there is someone who got rich selling them.

Good point, Trimitek

After 2 years , how much do you earn average in a month ?

You should look at the highest earners and see what they produce in terms of quality and how much they sell their models for. Look at creators already making what you are looking to make. I can say through my research that very few creatives make $500 dollars a month on their own.

Daaamn...
Two years later there is still not even one spaghetti sandwich 3d model!
¯\_(ツ)_/¯