You absolutely can begin detailing for money with a $300 startup budget:
City/County Permit $45.
Meguiar's Deep Crystal 3 Step 16 oz. set $22.
Poorboy's World Leather Stuff $18.
Poorboy's World Super Slick & Suds Car Wash $16.
Poorboy's World Air Freshener (choice of scents) $12.
Poorboy's World Trim Restorer $15.
Stoner Invisible Glass $6.
Stoner Tarminator Bug and Tar $6.
Stoner Reach and Clean Tool $17.
Lake Country CCS Hand Applicators Trio $10.
Cobra Microfiber Multi Pack $25.
Sams/Costco Microfiber 24 Pack $10.
Carrand Deluxe Tire & Bumper Brush $12.
Carrand MF MAX Wash Mitt $8.
Carrand Double Loop Wheel Brush $7.
Glass Science Glass Scrub $6.
DP Total Interior Cleaner $16.
DP Interior Surface Protectant $17.
Home Depot 5gal Bucket $3.
Home Depot 50' Hose $25.
Hose Nozzle $4.
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TOTAL $300.
sources: Home Depot, WalMart, Autogeek.net (be sure to look for Forum Member Discounts, Free Shipping Offers, Sales, etc.)
Many of us started with less than this list.
Best of luck, Michael. Go for it!