Tibia Coins price is hard to determine because there are a lot of factors that can cause it to increase or reduce the price.
The factors you need to consider:
1) Is it GBE or YBE?
Green Battle-Eye Worlds and Yellow Battle-Eye Worlds are totally different in terms of economy, since the Yellow ones are old and players on these Worlds gathered Gold for a lifetime. The best example is Antica, which you can pay 1kkk on a simple house competing with others, while on Green you have lots of houses available and the World don't have that much Gold, that's why the Tibia Coin price is lower.
For example, on Green Open PVP/Retro PVP that are already available for server transfer, the Tibia Coin price today (21/06/2024) is between 29k and 31k. Before it was 32k-34k, but after CipSoft announced the new items cost increase in the Summer Update, players started to panic and stock huge loads of items (Stone Skin Amulets and Might Rings), meaning they bought a lot of Gold with Tibia Coins, making their World economy change, thus reducing the Tibia Coin price to roughly 28k on a specific day that I don't remember. CipSoft actions toward inflation makes the price decrease. Considering your current situation, you must be playing on a new World, that's why the Tibia Coin price on your world is low. The price will always go up no matter what happens, until the new Worlds are opened for transfers and then the price stabilizes and become the same as other Worlds of the same PVP type.
But the Tibia Coin price can still decrease depending on some factors. On Double Weekends, where the Double Skill event is activated, people who train on Dummies with Exercise Weapons will buy it depending on the Tibia Coin price.
If the Tibia Coin price is lower than 10,5k, they will buy the Exercise Weapons with Tibia Coins.
For example: You want to buy a 8 hour Exercise Weapon, the Tibia Coin price is 9k, so it's better to buy it with Tibia Coins, because it's cheaper than buying it with Gold (which counts as 10,5k minimum Tibia Coin price to be worth it to buy with Gold).
The Coin price is 9k -> If you have 0 gold and try to buy the required 7,560,000 Gold with your Tibia Coins, the amount you get buying Gold with Tibia Coins is going to be lower than the required 7,560,000 and to reach that amount, you will need to pay more than the 720 Tibia Coins (Price of the 8h Exercise Weapon on the store), so it's better to get it on the Store. After the Gold value surpasses the 10,5k mark, then it's better to buy the required 7,560,000 Gold with Tibia Coins to buy it on the NPC, with each weapon costing less than 720 Tibia Coins overall.
On Double Weekends, the price is determined by the 10,5k Gold mark. New Worlds the coin price starts very low and go up fast, so we have some "events" in the game that can increase the cost.
2) Rashid - When a new world is launched, it's usually on a Wednesday. The first week economy is determined by Rashid, since he buys lots of items that are dropped on hunts. When the World complete a full week (From Monday to Sunday) and players complete his quest, the coin price increases a lot because all those items that were looted before, when selling them, makes the server get lots of Gold and the demand for selling it for Tibia Coins increases, increasing Tibia Coin price.
3) Yasir - Since Yasir is a Mini World Change, he is not always available, but he makes the World economy grow faster because people sell lots of items and puts up lots of Gold into the server, that's why when he appears, the Tibia Coin price gets a spike on the price. I didn't played enough on YBE worlds to know if Yasir appearing makes the coin price go up, but on GBE and with the coin below 10,5k, he certainly makes the price increase.
If the Tibia Coin price on your world is 12k now, it can still decrease on Double Events, because people will prefer to buy Exercise Weapons with Gold, and when they buy the Gold that is available on the Tibia Coin Buy Offers, the price decreases, because they are burning that Gold and the demand is high because of the event.
The Double Skill event makes the Tibia Coin increase when it is lower than 10,5k, and also makes it decrease when the value is higher than 10,5k.
Lower than 10,5k -> Players need Tibia Coins to buy their Exercise Weapons, since they are cheaper, so they sell their Gold for TC to buy them from the Store.
Higher than 10,5k -> Players need Gold to buy their Exercise Weapons, since now they are even more cheaper than buying it with Tibia Coins (if the Tibia Coin price is 30k for example, you can buy almost 3 Exercise Weapons from the NPC with the price of 720 Tibia Coins if you exchange it on the Market, making it way more cheaper than buying 1 Weapon for 720 TCs).
There are also other factors like Double Experience, where people buy lots of Exp Boosts, so everything counts.
There is no "correct answer" to your question, since it depends a lot on the World's own economy and also on CipSoft's actions. Treat it like if it was the real world economy, since everything that is happening day by day is what determines the price.