Hi Rebjane, yes it is expensive! My insurance paid 80% and I have to pay for my replacement aerosol heads out of pocket, however I STILL feel it is the best nebulizer I've ever had and due to all the time saved and ability to take it with me anywhere (it runs on rechargeable batteries too), I feel it is worth the cost and the small hassle of cleaning.
I'm not sure about the formal recommendation on using different aerosol heads, but I mostly use the same one in one session as I figure I'd be getting the same level of residual medication mix as in a compressor neb. I do empty out + wipe out the medication chamber before adding the next med.
The only exception to this is that while always I use hypertonic saline in it, I feel like the salt causes the most damage to the aerosol head (I might be imagining it). So in the session where I do the HTS, I sometimes switch to an older aerosol head just for HTS, and then back to the 'good' one to finish the abx.
Cleaning it is a bit of a process but there are ways to make it easier. I have a little electronic egg boiler, the kind that takes 7 eggs and you pour water in and it steams for about 5-10 minutes? It's just the right size to fit 1 neb so I use this to sterilise the plastic handset and aerosol head since you can't sterilise in the microwave due to the metal in the aerosol head. Note, this is just a hack I came up with NOT what they actually recommend for cleaning. There is also a 'backwash gadget' that came with mine where you reverse clean it and this helps maintain the aerosol head, this I only do once or twice per month.