From what I hear, the investment is worth it..
If you want to cut corners a little but still get an *AMAZING* sounding monitor (in the way that monitors sound amazing, good on good stuff, terrible on bad stuff, yknow) look into the Kein & Hummel O300s. They go down to around 40Hz evenly (without a sub) and drop off quite nicely below that. They thump insanely... I actually wouldn't get anything subbier for a home studio environment. These absolutely played havoc with untreated rooms. They sounded stellar in larger rooms with treatment/diffusion, but absolutely terrible in smaller untreated rooms.
Not an NS10 or BM5 fan here. The BM5 sounds a bit like a boombox/hyped stereo compared to its more neutral cousin, the BM6. I've tried some BM15a's too but they didn't do it for me. NS10's are just... I don't know how people can bring themselves to listen to them 8+ hours a day. My ears wanna commit suicide after seconds.