Something you need to take into consideration what kind of tracking mechanism does the Dobsonian telescope you're looking at have?
There are apparently several different types and manufacturers so there are going to all kinds of different user interface options involved. There's going to be a lot of proprietary restrictions so it's unlikely any 'app' or any 'web site' you choose is going to work with all of those different mechanisms. Most will need to be supplied by their manufacturer. Your Celestron 6E has its own built-in computerized tracking mechanism to aim itself and tie into an online interface remotely. Finding that same kind of convenience might take some more effort with whichever Dobsonian model you intend to buy. But a plus point is in today's market, online access and connectivity is so prevalent there's a good chance your new telescope will have some solid backing by its manufacturer so it will include at some kind of app or web site for it.
Regarding a secondary phone or tablet just for your new telescope, I'd recommend you avoid low-balling it too much. Cheap knock-offs typically involve budget-quality hardware among other limitations. That Astrohopper web site for example will be relying on a lot of working, dependable sensors in the phone or tablet. When you're out in the field away from a usable WiFi network you'll need cellular connectivity so you'll need a tablet that includes a SIM card slot. That rules out cheap tablets as most of them that do include both WiFi and cellular support tend to be pricier. As for either a phone or tablet, you'll need to have mobile data and Location enabled so GPS in conjunction with current star maps can feed the telescope's tracking mechanism with accurate data. Cheap phones may skimp on the all the required sensors among other things, so you may save a little cash up front but the time and extra efforts you'll waste fighting with a cheap, low-spec phone just to do basic tasks is going a long-term cost on your mood. One viable option is to buy a carrier-locked phone directly from a carrier. They often sell them at very low-cost or even free, the caveat being it's going to be carrier-locked (to the vendor) and involve a contract. If you're happy with your carrier and plan on staying with them for a few years anyway than that's not problem. Just be selective about which phone you choose because they offer a lot of cheap, crap phones along with some really nice models too.
