First thoughts of a requirement engineer

So, how should TreppenSchlepper look like, what exactly should it do or provide? What are the mandatory requirements, what would be just nice to have, and what would be a killer if we forgot about it ?
The importance of good requirement engineering can hardly be overestimated, as it does a lot to define (and constrain!) the direction a project will go from then on. Even if done iteratively in an agile development process, someone better has a consistent, solid view and vision of what the system under development should look like. And defining such vision on non-functional requirements or "soft facts" might sometimes be even more important than getting all technical requirements right from the beginning.
So let's add some thoughts on the user interface (UI) and target costs.

First: do we need an UI at all? If it comes to path planning and climbing stairs, TreppenSchlepper should be fully self-controlled, thus autonomous. No human operator should be required to control its moves (please, please, no RF remote control like a toy car!). TreppenSchlepper shall detect and analyse its surroundings completely by itself, plan its path, control its movements, know when to stop, and therefore guarantee system safety at all times by itself.
However, we need a way to summon it to the place (e.g. floor number) where we want it to start, and tell it where to go (e,g, come to base floor, wait until I've placed my heavy bag, then carry it up to 2nd floor, then wait until I have recovered my bag). The obvious choice would be a smartphone app, communicating with TreppenSchlepper e.g. via BlueTooth. Is that a good idea also for people feeling uncomfortable with such gadgets? We might want to provide an alternative solution like a button on a wrist-watch (similar to the Personal Emergency Response System (PERS), but not that dramatic). Would BlueTooth provide sufficient transmission range to connect to TreppenSchlepper in a staircase, even if it is lots of floors away?  And, let's assume one wants to call (summon) TreppenSchlepper to a certain floor: we sure want it to detect automatically where to go; so how would the calling device (e.g. the smartphone) identify its current floor to send it to TreppenSchlepper (and vice versa)? Maybe a system of fixed BlueTooth stations acting both as location beacons as well as relays, forwarding calls, might help. Something like iBeacon, maybe? 


Next: Pricetag

A conventional stair lift in a museum in Berlin

TreppenSchlepper is intended to just carry things, rather then persons, at least in its initial incarnation. But it should be also much more flexible and easier to use than e.g. stairlifts, and should be more affordable as well.
According to https://en.wikipedia.org/wiki/Stairlift today's stairlifts start at 2000 - 4000 USD (and that is per floor!), even others suggest € 4.000,- to € 14.000,-,
Still keep in mind that this is for full person-carrying capacity. So I'd suggest an upper price limit for the described TreppenSchlepper of below 2000€, which might make it competititve, as this is independent of the number of floors to cover. 
Is that an achieveable price limit?