I don't have an ALPY but know a bit about it....it comes in three flavours - the basic module then the entrance slit module then the guiding module....sure you could start with the basic and then spend more money later....
If you haven't tried spectroscopy then I'd recommend starting with a filter grating either the SA100 or the SA200 (The SA200 is more suited to shorter spacing between the grating and the CCD -like when mounted in a filter wheel)
The grating will get you started - "Spectroscopy 101"
It gives you the opportunity of gaining practise in obtaining a spectral image then coming to terms with the necessary processing software as well as learning what spectroscopy can show you .....
After that experience you can decide whether or not to invest more money in an ALPY, or LISA or even a LHiresIII.