I'm looking at some clothes to wear while I'm biking, and I saw that some jerseys/shirts have little sacks/pockets on the lower back.

Do all jerseys have this? I would like one of these so that I can stop wearing a little sling bag to carry my stuff.

yes

i like the ones that also have a little zipped pocket either inside or outside one of the bigger pockets. good for credit card and money.

Yeah most bike jerseys have those three pockets in the back. I carry all my stuff in my pockets now and it's pretty comfortable. On Tuesday I carried all my stuff normally and a full 20oz water bottle and it was still comfortable.

Also my Champ-sys bibs come with a small pocket that lays right between my shoulder blades. I'm guessing its for an mp3 player.

It's for a race radio, but obviously you can put anything in there that fits.

Those pockets are there so you can carry guns and lots of ammo, for self protection ofcourse!

New rider? Likely.

Those are cycling jerseys. The pockets are there to hold tubes, C02, food, money and anything else that you need. This takes the place of a saddle bag (which you don't need).

Buy one or 2. Only ride with them.

Yes

Would it be reasonable if I am thinking of getting a jersey for ~$50?

yea..... some jersey ride from $20 to $100 your choice.....

also check Performance... they have great deal once in while...

https://www.performancebike.com/bikes..._400000_400000

Went to my LBS today, and I tried on some jerseys

Most were in the $80+ range.

I tried on a Castelli (?) jersey. Seemed nice, $80. Is this alright?

The reason I prefer to buy from a brick/mortar store is because I can try the jersey on before buying

Castelli makes some nice stuff. Some of their jerseys are worth $80.

If you're just looking for a basic jersey you can do better than $80, though, even at a shop. I'd try looking at a different one.

$80 is about right for a jersey. You can get em much cheaper, but I'd rather shell out the extra dough and get something I actually like.

If you buy online, you can buy several sizes and try em all out. Keep the one that fits and ship the rest back. USPS medium flat rate boxes cost $10.70 to anywhere in the US and can fit a boatload of jerseys. 70 lb weight limit which you won't get anywhere near.

Consider getting a base layer shirt as well. In addition to the added comfort, it keeps the expensive jersey cleaner so you don't have to wash it as often.

https://realcyclist.com has some good deals on castelli

Twin Six makes some nice jerseys that won't make you look like a billboard. My only beef is the 3/4 zipper - the bottom end causes me irritation. Kinda wish they'd go full zipper. Their jerseys will run you about $70.

Might want to look into getting a saddlebag first while you build up your collection of cycling jerseys.

I like to have a saddlebag to carry what I need to fix flats. I don't like to have tubes and tools in my pockets. I prefer to buy jerseys online because of the (relative to local shops) low cost and broad choice. It's very easy to buy jerseys online at favorable prices. Most dealers have liberal return/exchange policies.

keep an eye on Nashbar.

I snagged a $120 jersey on sale for $40.