You can pay monthly or annually for subscriptions. Monthly plans are the priciest, except for the Essentials Standard subscription which costs the same regardless.
Online store payments are not handled by BigCommerce. In fact, you can choose to integrate any of 20+ payment gateways such as PayPal or Adyen. BigCommerce does not charge you for online transactions, so you only pay the transaction fee applicable to the chosen payment provider.
Subscriptions have tiered features, with only standard features on the cheapest plan. For instance the cheapest (Standard) plan does not send abandoned cart emails, while product-filtered search is only available on the Pro plan (which could be a deal-breaker for a cash-strapped, inventory-rich boutique).
Where BigCommerce differs from other online stores on this list is the limits they impose on online sales for each tiered plan. That is, you can max. sell for up to US$50k annually on the Standard plan, $180k on Plus and $400k on Pro.