1 · Software subscriptionEntry retail plans run $0–$99/register/month; serious multi-feature plans run $100–$300+. Watch for per-register multipliers and add-on stacking — a "$69" plan across three registers plus payroll and loyalty add-ons is not $69.
2 · HardwareAn iPad-based system reuses hardware you own; proprietary terminals cost $500–$1,700 each or come as a lease that outlives your patience. Receipt printers ($150–$400) and scanners ($100–$300) are similar everywhere.
3 · Payment processingThe quiet giant: 2.5–3% of every sale. Systems that lock you to their processor take away your ability to negotiate — on $40k/month of card volume, half a percent is $200/month, every month.
4 · Add-onsPayroll (+$40–80/mo), loyalty (+$25–45/mo), marketing (+$30–100/mo), advanced reporting, extra users… This is where "cheap" systems get expensive. Price the features you'll actually run, not the entry plan.