At one property manager and a handful of jobs a month, a phone camera, a shared folder, and a spreadsheet will hold. The dolly is the better spend.
What you'll eventually pay for, and roughly what it runs. Invoicing and bookkeeping software sits in the $20 to $70 a month range for a small operation, and you want it earlier than you think because commercial clients pay off invoices with numbers on them, not text messages. Field service apps with scheduling, crew dispatch and before and after photo capture generally start around $30 to $50 per user per month and climb from there, and they earn their keep once you have crews you can't see. Some clients run their own vendor portal at no cost to you, but the portal will dictate photo counts, file naming and upload deadlines, and missing those is how invoices get held.
The habit that matters more than any tool is the photo record. Date-stamped shots of every room before you start, the loaded truck, the scale ticket or dump receipt, and the finished rooms from the same angles as the before shots. Keep them per property in a folder named for the address. That folder is what you send when someone disputes the scope, and it's what a servicer will ask for later if you move into REO work.
One more thing that catches people who start with turnover cleaning: cleans and haul-offs are different jobs with different costs. Track them separately from your first invoice or you won't know which one is paying you.