What exactly are bicycle clothes? The tight stuff I see people wear that look like the compete in races? My fat a$$ isn't going into that clothing. If I am riding for exercise or fun I just wear shorts with compression shorts and tshirt. Which is something I am struggling with for riding to work because I wear boots. I have my exercise shoes but not everyday wear to work ride a bicycle in shoes. So now I need to buy shoes? Sigh. Starting up bicycle riding can get expensive it seems.
No specific clothing is really necessary... When I started commuting I was just in a cotton T-shirt, some old athletic shorts, and tennis shoes (10 mi each way). I certainly wouldn't go back, but it was fine for a while. After a year or so those were pretty shot so I got/was gifted some new things. I still don't really have much bike-specific gear, just some more breathable shirts and a couple things like gloves and other cold-weather gear. I found that clothing made specifically for bikes cost about 3x as much as something similar that was more generically athletic clothing. Maybe I was just looking at the wrong shops though. The breathable shirts were definitely the best bang-for-the-buck during warm weather. Mine aren't even tight really.
General purpose athletic clothing is good, but if you care about
One nice thing about purpose-made bicycle clothes (of which I currently own none) is that the pants are cut higher in the back and the tops are cut longer in the back so your bum doesn't hang out too much. More of an issue for tall/long-torsoed people, but it's definitely nice to have sometimes.
then only cycling clothing is going to fit the bill (at least, as far as I know). Which I do care about on a particularly windy day.
For commuting my 3.1 miles I don't go very fancy, jeans, t-shirt, over shirt, running shoes, and rain gear. Even my rain pants aren't cycling pants, just the cheapest pair I found on Amazon.
For cycling on the weekends where I do the 30+ mile rides, or like last weekend doing 75mi the bike specific clothing is really nice to have. Specifically the jersey I just got is awesome. 3 Pockets in the back to hold cellphone (including backup battery), stuff, and food (going left to right) which is easily accessible while riding. The shorts I'm still not totally convinced they make that big of a difference, I was riding 30+ in kahki before getting cycling bibs. The only really big difference is that being skin tight there is less drag, and won't get caught on my chain or bottle holder. My rain coat (GoreTex, spendy, but keeps me dry) is cycling specific and has longer arms which happen to come up to just about my wrists when in cycling position, but are slightly long when not riding, and gets used for both commuting and recreational. My cycling shoes came with the bike when I got it, along with the SPD pedals.
I try to find the clothing as cheap as possible, but since I only wear them while cycling long distances I figure they will last a long time and if my hobby is cycling for recreation then spending a little bit into it isn't bad, but I weigh each purchase (not for cutting grams) with the utility it will provide. Right now I'm thinking of a cycling specific GPS because going 75mi I went through my cell phone's battery, as much recharge I could get while at the destination, the backup Anker battery (single full charge), and got home with 3% battery left. I'm giving this hobby time to make sure I'll be sticking with it before putting a lot in, which considering my recent bike purchase last year I'm pretty sure I'm past the point of putting a lot in. Nashbar has been a good source for cheap cycling clothing, combined with 20% off coupons and free shipping.