You don't need a service provider other than a "contact person".

The actual minimal cost of getting e-residency is a one time €150 state fee (I guess you have to renew the physical card every 5 years, which is €150 again?). If you also want to incorporate an Estonian company (which you probably do in this context here), then the registration for this is a €265 one time state fee.

There are no other mandatory fees, except you have to find a "contact person" who's responsible for receiving official government communication on behalf of your company (don't worry, I have never gotten any physical communication from any gov agencies during my 10 years of having a company here so this "contact person" won't actually be doing anything and is just a formality). After a 3 minute google search, this service can be had for €7 / month.

If you don't want to file taxes yourself then you'd also need to hire a local accounting firm. That'll start from somewhere around €50/month for a micro-SaaS. If you really want to, you can file taxes yourself for free but.. your call if your time spent learning the Estonian tax code is worth the saved money..