Welcome!
The cheapest way is probably to treat it like a tent on wheels. Just be sure to secure stuff so it doesn’t move while driving.
Camping gear works great, and it’s usually cheap this time of year.
Plastiic drawers are a great addition, and with a wood shelf on top can create a counter top or work space.
A DIY heater/cooker can be built from dollar store parts for $5-$6. Walmart has kerosene lanterns for under $10. Get car cords to charge your laptop/phone from from your cigarette lighter outlet. Use a 5 gallon bucket to make a bucket toilet.
Dollar store dish pans, and trigger spray bottles for your sinks & water delivery. The water can be warmed on the stove, or sat in a window for sun heating.
A hula hoop makes a great shower curtain rod to enclose your bathroom. A foldable doggie bath/pool can catch your shower water.
A patio chaise lounge can make a great bed. TV trays make very handy portable tables. Bed trays make good lap trays, and can also be hung with a little rope. I sometimes use this on my steering wheel, or to hang on the inside or outside of doors. Cheap throw rugs can solve cold floor problems. A sleep mask can make it night time at any time of day. Cover your neck, head, & ears if you get cold at night. Balaclava’s & ski masks work great. If it’s too cold, I’ll sometimes add ski goggles.
USB rechargeable fans can be great. Solar powered garden/stake lights can be be a great addition too. Recharge in a window. When your budget improves, I love my solar powered bug zapper.
Everything can be done extremely cheaply without sacrificing comfort or convenience.
Later you can add a house battery and an isolator to charge it while driving.
Walk in day labor usually has work, and same day pay. Temp services if you’re staying longer and have enough money to last through to a payday.
Online businesses are cheap to start, and can be very lucrative. I average $1,000 a day working between breakfast & lunch, making simple web pages for $100/ea. I turn away more business than I take. There’s over a million new businesses every year, and most need affordable business services. One of my traveling partners resells outsourced new business advertising packages, and has made over a million so far this year. We are work from home traveling nomads.