Hello and thank you for your question. Based on your description the business has enough cash to purchase the trailer as noted $4,000 in sales and $600 in expenses, specifically start up. If trailer is purchased I would look into possible section 179 deduction or capitalzing and depreciating over the useful life of the trailer. If Section 179 is utilized, the full purchase price will be used or you can choose to depreciate over the useful life of trailer. I will insert link to clarify more on Section 179. Have a great day!
From TurboTax "What is Section 179 deduction?"