Hate to be bursting a bubble here, but your parents are very correct.
Look at it this way... what kind of job can you get right now? What will it pay?
Lets be generous and say you land an entry level job at $8.50 / hr. Well, if you want to go to school, that will take 8 hrs of your day. Then add another 2.5 hrs per for studying (this is a minimum! - college courses expect 2 hrs per hour spent in class!). That uses a total of: 60 hrs/wk. That means you have 168 hrs left in the week to figure out working, sleeping, eating / rec time. Well, you'll need to work 40 hrs/wk just to get by, so now you're at 128 hrs, which equals about 18 hrs per day average.
At 8.50/hr, 40hrs = $340. Expect take home to be 3/4 of your actual, $255/mth. That comes out to: $1020 monthly to spend.
How much are you paying in rent? You'll be lucky to find someplace under $400. Lets be generous and say $350.
Utilities usually start around $100 /mth (NOT including internet)
Have a cell phone? Well, average is $50/mth
Have a car? Insurance starts around $100/mth for an 18 yr old
Well, that leaves you with about $420/mth for food, gas, and "extras" (internet, cable, landline, clothing, etc). That comes out to $105/week - and this is assuming you can get rent as cheap as I have described. I know you can't count on that near Lansing, and it only gets more expensive with larger cities.
Then, theres the medical insurance... as an 18 yr old living on your own, you are not entitled to be on your parents coverage. Most entry level jobs don't offer it, and if they do, plan to pay out at least $60/mth for yourself. I'll tell you my experience... when I was 18 I had several ER visits because my body was changing, and each of those visits were no less than $1000 in cost. Thank goodness I had medical coverage through my dad! Once I was off his, I had 1 ER visit for a broken hand (mountain bike crash) that cost me $750, and 1 ER visit for stitches (cut my hand while opening a can of cat food) that cost me $900. That was my out of pocket expense.
What happens if your car breaks down? Can you afford the repairs? My last major repair was an ingnition coil and it cost me $300 to fix. Before that was a ball joint, $160. Before that, wheel bearing and brakes, $400. Currently, need another new ignition coil (different car), new radiator, brake pads, and time spent with the mechanic to find out why our truck stalls out when idling ($55/hr).
I moved out on my own when I was 19. I was making $10/hr at that time and had to drop out of college because I couldn't keep up with my coursework. Despite the money I was making, I still HAD to have a roommate. In fact, I'm 26 now and have never lived completely alone - because it hasn't been an affordable option! At this time, I'm married (and we paid for our wedding with no help - we opted out for an el cheapo ceremony and spent a total of $200) and I have my husband's income.. but with more income comes more responsibilities .. a 2nd car, more car insurance, more food, more medical bills, more clothing, a 2nd pair of eyeglasses, etc, etc.
You might not know it, but your feelings are TOTALLY undestood! But, remember this... what your whole world revolves around right now is going to change very, very soon. Talk to the rents to see if there can be a compromise ... but, otherwise understand they want the best for you and they know how hard it would be for you to try being on your own. You'll work non-stop, probably have to hold 2-3 jobs, work nights, lose sleep, and watch your grades suffer dramatically. You won't be able to spend much time out with the friends you don't want to leave... is it worth it?