How can the costs be too high vs using a service provider? Most likely every service provider will take a % cut, which, if i somewhat understand what you're trying to do, would be detrimental.
Why not get a VPS for a couple bucks, (EC2 = ~20$ p month), and use core RPC? I can almost guarantee it will be less of a hassle than using something like coinpayments (which is not meant for this anyhow)
My goal is to create a micro-wallet system for small value transactions avoiding fees from the Blockchain network. I know that the best option would be to host the wallets on my own server so as not to depend on third party services, but for the time being this option is not viable because the initial cost will be high.
Coinpayments taking a 0.5% cut on each payment would be cutting your margins significantly - plus i'm not sure if their API actually broadcasts payments, and if they do, you'll still probably need your own DB to keep track of each individual account/address.
In fact, hosting my own NODE would be ideal. But at first my goal is to use a third-party service, to facilitate integration and test the idea without having to delve into more complex technical knowledge at this early stage.
Because to follow this path it would be necessary to have several Nodes, one for each currency, which makes everything very complex. At this initial moment, I want something simpler and faster to be used, later, with the results of the project in hand, it would be the most appropriate time to implement my own solution with lower cost and higher performance.