If you need to track income, expenses, invoices, and time, you'll likely be paying $35/month for QBO or $60/month for Xero. For the top plans, you'll get similar functionality from both providers.
Xero pricing
Xero offers three pricing tiers, ranging from $9 per month to $60 per month.

Xero's most basic plan (Early) comes at a tempting $9/month, but you're very limited with the feature set. You can only send 5 invoices and quotes, enter 5 bills and reconcile 20 bank transactions. For most businesses, this isn’t going to be enough.
Their mid-price plan (Growing) will fit most small businesses. You can send invoices and quotes, enter bills and reconcile bank transactions for $30/month.
For the full feature set, you’ll need Xero’s top plan (Established). For $60/month you get all of the Growing features plus multi-currency functionality, expenses (to capture and manage claims), and projects (to track project time and costs).
If you want access to their Gusto full-service payroll (available across all 50 states for US customers), pricing starts at $39/month base + $6/month per person.
If you're outside North America, you can access country-specific payroll as an add-on in some regions, including the UK.
QuickBooks pricing
You can get started with QuickBooks Online from $25 per month as the lowest of three price plans.

QBO’s basic plan (Essentials) starts at $25/month. This comes with much more functionality than Xero's cheapest plan, including all the basics of tracking income and expenses, capturing and organizing receipts, invoicing and accepting payments. You also get access to basic reporting. The main limitation of QBO’s Essentials is access for only one user. You also can't track time and inventory.
Many businesses will go for the Plus plan at $70/month, with all of the above features as well as access for up to five users, time tracking, inventory, and access to more reporting including for project profitability.
As expected, the fancy features come in the top plan: Advanced for $150/month. This gives you access to features such as batch invoices and expenses, automated approvals and reminders, management reports and fields, and custom reporting fields.
For payroll, you have three choices of add-on: Payroll Core, Payroll Premium and Payroll Elite, ranging from $45 + $4/employee/month to $125 + $10/employee/month.
All plans also include receipt capture, expert support, and out-of-the-box integrations.