If you need width, this one on Amazon is 22in wide instead of your standard 20in.
Big 4 for $502
The rest of the gear is relatively cheap, like:
Random stuff from your house / DIY:
Clothes could be a whole post of their own. Start with what you already own and upgrade to wool/synthetics over time.
Food from the grocery store is cheap. Skip the fancy freeze dried stuff. Shout out /r/trailmeals.
Skipping unnecessary items is the best way to save money. Amazon will make you think that a huge knife, lantern, chair, axesaw, and other 'camping' gear is important. Don't let them trick you into wasting money / weight on garbage.
EDIT: added a few items
Super important.... The entire sleep system, not only the bag/blankets... Make sure you are using an insulated sleeping pad or some type of foam. A normal, inflatable, sleeping pad has almost no R-value(temp rating) unless it is branded as insulated. One way to help increase the warmth is by adding a folding sleeping pad on top of your inflatable pad/mattress(Affordable insulated pad) and what I have done is wrap a wool blanket and a synthetic down blanket around the inflatable mattress and the folding pad. This along with my sleeping bag, fleece liner and possibly another wool blanket(if needed) has seen me through nights reaching the upper teens and low 20's. Throw in some water bottles with hot water or even a few hot hands to add some extra heat sources. Also, personal tip as I sleep hot and don't sleep with socks on normally, I always keep my socks and base layers in the sleeping bag with me so that I'm not trying to find those in the car which have gotten cold through out the night. Worse thing is to wake up and have to put on cold layers before getting out of the car and getting fully dressed. HAPPY CAMPING!!!