I am planning to buy a bike but they don't have my exact size. My bike size is 52cm but the bike I plan to buy only comes in 50cm and 54cm. Which size would be better for me? 54cm might be a little to big for me and 50cm might be a little to small.

Why are you planning to buy a bike that doesn't fit?

Because Saephan215 is a rebel.

If you are sure your bike size is 52, this is the size you must have. buying smaller or larger bike that you need will not work.

It's like asking: "I have my shoes size 8. Should I buy size 7.5 or 8.5?"

Also, want make and model bike you are looking for? I have a hard time to recall bike brand that steps up from 50 to 54 completely missing 52 size

This is a pretty bad idea. But if you persist, I would say a 50 with a long stem probably is the least bad.

Would you buy a pair of shoes that don't fit? Pick a different bike or find another store that has the bike in the size that fits.

https://www.amazon.com/54cm-Vilano-TU.../dp/B005EFTQ9C

This is bike I am planning to buy. I'm on a budget and looking for a road bike around $250.

are you guys honestly telling him that he wont be able to ride a bike that is 2cm larger or smaller than his normal size?

This might work for you.
https://philadelphia.craigslist.org/bik/2802144701.html

2cm makes a bigger difference than it may seem like, particularly in the frame. I would much rather get a used bike on Craigslist that fits. Good chance of getting a better bike as well.

For casual riding I'm sure it works. I supposes I could run with shoes a half size off either way, but it just wouldn't be comfortable for anything serious.

I'm not sure that you can find any new bike at $239 that is going to last. At least this looks better than the no-name brand big box bikes. Perhaps you can find a half-decent bike on Craigslist for that same money. I would look for reviews of specific bikes from Bikesdirect in your size.

You are more likely to enjoy riding your bike and ride it more often if the fit is better.