Or is it more expensive to buy penny stocks?
Depends on the broker.
For many brokers, you have a set fee for each transaction – no matter if you buy 1 share or 10k shares. Sometimes, the brokers will cap out how many shares you can buy with one transaction – mine is 5000 shares.
Many brokers also have commission structure where you pay a certain amount per share. I think the rate is about .01 per share. If you are buying a lot of penny stocks, the commissions could add up pretty fast.
As a suggestion, when I was first starting out, instead of buying penny stocks, I looked to buy options on more expensive and volatile stocks. Penny stocks always seemed too risky for me. Either way, make sure you practice TONS before putting any money at risk.