It's no longer a particularly competitive card, and it's far from the most valuable Charizard card in history
In terms of speculating on this, I think that anything under or around $10 is a solid buy to hit $20+ in the next 12-18 months demand for this isnt going to be huge, but supply isnt exactly on the high side either and so as people upgrade their copies, the price is going to get dragged upwards
For example, one card may be worth $0.10, and another may be worth over $100,000
With three colors itll cost quite a bit to optimize your mana base, and its up to you to decide how important that is
Most people with resources knew that every previous card with you may have as many copies as you want in a deck had gotten expensive, so Approach never settled down