Many domestic espresso machines have just one boiler, often above and attached to the group where coffee is made.
You can usually spot them easily enough as there is a switch that heats up the boiler enough to make coffee, another to "super heat" the boiler to produce steam to enable the frothing of milk.
Personally, I'd avoid these! They often make a decent enough espresso but by the time the thing has heated up its tiny boiler to a point where a pathetic amount of steam is available the espresso has gone cold before you can heat the milk! If you try using more than a cup full of milk, frothing can take ages too.
When you finally get a cappuccino you'll no doubt be asked for another. Re-priming the boiler, waiting for it to heat and then repeating the process for steam is enough to drive me crazy.
If you want to save some money, I quite like the Pavoni range of domestic lever machines, "Europiccola" models. With a bit of practice (YouTube has plenty of videos on them) you can get some great results. They look pretty cool, easy to service and repair and it will leave you with cash to buy a nice grinder? Oh, and the boiler produces a decent amout of steam that's available without having to wait after making espresso...
