You should not think about it in terms of amount invested. As someone new to investing, you should only consider two things:
- Potential ROI
- Transaction Fees
Potential ROI is return on investment. Whether you put in $25 or 25,000, ROI is important. However, when you're investing smaller amounts, you can take more risk. Look for a token that has the potential for 100-1000% returns. Bitcoin is "safer," but the return on 25 if it goes up 10% over the next couple months is $2.50. Not much as you can see. Try your hand at something more risky!
Transaction fees are not usually an issue on exchanges, but there are sometimes purchase minimums so keep that in mind. However, Bitcoin is not fungible currently, which means here that it isn't easily divisible into small amounts. Sometimes, Bitcoin can cost up to $10 to send to another address. So if you send your bitcoin to someone else, you would only be able to send $15! That's a loss (friction) of 40%. Not a good thing...
If I were you, find a cool token to invest in without question.