Use pre-built DNN modules provided they satisfy both your requirements and budget.External services that must "talk" to your DNN website require integration code placed on your website that interfaces to other services.Registration, shopping cart or other order forms are typically modules installed to DNN that interface to external payment providers such as PayPal, Stripe or Authorize.net. The installed module provides the main functionality and when configured with your account details, can reach out to PayPal, MailChimp, etc. for processing your data.Using the examples above, consider how modules such as shopping carts typically store their data on databases provided by your web hosting provider. Where modules display locally BUT store data externally, you must access your data from the external site. i.e. The MailChimp sign-up might be done on your website but the user is added to a list stored on MailChimp list servers.The cost of hosting the data and maintaining backups depends on the size and location of stored data. In the case of MailChimp your lists are stored on their servers and interacted with from their interface. So your plan with them covers these costs. Separately, you might have paid for a DNN module that allows your DNN site to submit NEW leads to your MailChimp contact lists. Just remember, data stored externally is not backed up as part of your DNN website.
Where no suitable module or service can be found you'll need a software developer specializing in DotNetNuke. Perhaps you need your DNN users to access their golf club membership in the database at the country club. A real estate sales firm may want their CRM to be aware of prospects gathered from their DNN website. Under these circumstances the possibilities, budget and costs are determined by the creativity and experience of your DNN module developer.For a free consultation or quote, contact Dylan at INNO Software. For expert DNN skinning and UI advice, contact Info at INNO Software.