Most of these videos have bad audio for some reason. Turn up volume. Closed-captions useful.
The value of ancient coins in general varies depending on their rarity, artistic interest, the value of their metal, etc. etc. Some Roman coins can be bought fairly cheaply -- many Roman imperial coins, for instance, can be purchased for less than $100, some for as little as 20 or 30 dollars from some auction sites.
One of the most collectible Roman coins is the sestertius. During the Republic, it was occasionally issued as a silver coin, but it was a much more common large brass coin in the Imperial period:
"The price of these coins is around $100 in some cases, but most of them in XF qualities are between $100 to $300. In the cases of certain emperors, and rarer specimens with incredible quality; the prices can shoot up to thousands and even millions of dollars," according to Collectionistas De Monedas.
Some coins are rare and expensive. The Roman Aureus, for example, was "a gold coin of ancient Rome originally valued at 25 pure silver denarii. The aureus was regularly issued from the 1st century BC to the beginning of the 4th century AD, when it was replaced by the solidus." (Wikipedia) The value of these coins seems to vary a lot depending on how many were issued under particular emperors:
"...some very rare coins can cost 5, 6, and sometimes even 7 figures ... This Ancient Tiberius Gold Aureus [next video], Certified by NGC in Choice Extremely Fine 5×4 condition is worth over $11,000. There are certain historical reasons that this coin is so rare and so desired." Source: Rare Coins Blog.
The gold aureus of Hadrian's period is also particularly valuable.
Some ancient coin collectors are generalists who pick up whatever they can find. Others specialize in particular periods, denominations and so on. For example, some enthusiasts try to build up collections of coins issued under each of the Roman emperors.
Collecting ancient coins is a huge field that involves a lot of research. Luckily, there are all sorts of online resources available. One good site is the Forum of Ancient Coins which includes a lot of information about Roman coins in particular, and the Classical Numismatics YouTube channel is really excellent if you can cope with the sometimes murky audio quality of its videos.
If you get into collecting ancient coins, one of the things you have to be aware of is that there are a lot of fake coins in the market. Strangely enough, though, some of these fake coins are themselves very valuable:
"Another main problem is represented [sic] by the fake coins. Ever since the XVI century, making fake coins for profit was profitable business. One of the most famous [counterfeiters] was the German Carl Becker, who lived in the first half of the XIX century. He had a special gift for this job and his creations are considered masterpieces, in some cases hard to identify as fakes. It is also true that today his fakes are considered to be more expensive then the originals but the fake is a fake." Source: Coins Auctioned.
"Unfortunately, today, some fakes are very dangerous for collectors. The fakes from the Bulgarian school are almost perfect in some cases. Also the Chinese fakes are starting to be more accurate then ever. Only with time and experience, these fakes can be avoided." Note: Both Bulgaria and China appear to be heavily involved in counterfeiting in general. According to one source I found, some of the Chinese fakes are actually worth collecting.
You should particularly be careful when buying ancient coins on eBay.