Sorry if this question is answered already somewhere on this site but I searched and could not find it.

What is the recommended air filter replacement?  I found a few options searching online and I am new to this so any advice appreciated.

This looks like the one I just took out.  However, the description says it's for '86 - '09 models.  Mine is a 2012.  Also, I would prefer Suzuki parts but if EMGO is considered a good brand I am fine with that:

https://www.amazon.com/1986-2009-SUZUKI-SAVAGE-13780-24B01-Manufacturer/dp/B0...

This one looks the same and comes with an oil filter as well.  No model years specified and brand is Hiflo filtro.  Again, I know nothing about that brand:

https://www.amazon.com/Filter-SUZUKI-Boulevard-LS650-FILTRO/dp/B01LW842CJ/ref...

This one looks very similar to what I have and is a Suzuki part but again, my 2012 model is not listed as compatible (which is really odd because years before and after ARE listed ... just skips over 2012 and 2013):

https://www.partzilla.com/product/suzuki/13780-24B01?gclid=EAIaIQobChMIpZjdmN...

This one does not look like the one I took out but my year model is listed.  It's more expensive but it says it's washable and reusable, so maybe worth it?  I have seen K&N discussed here so I am assuming reputable?:

https://www.partzilla.com/product/aftermarket/3LJI-K-AND-N-SU-6595

I have no idea how this one works lol!  Doesn't look like anything like what I took out.  Probably not what I am looking for but just curious how it would work:

https://www.partzilla.com/product/aftermarket/1ACG-HIFLO-HFA3608

Also, in general there seems to be quite a range in price, from 20 buck for air and oil filter to 80 bucks for the K&N.  What is the reason for the range?  Is it a 'you get what you pay for' kind of thing?

Oldfeller's air filter ,is the only  one I've used on my bike for the last four years, open, simple, better filtering than K&N , reusable (I'm still on my first) and very low cost (about $10.00-$1500 and you make it yourself). It's listed on this site , in the Tech Section.

The K&N Filter for the S40 it total shite, it does not fit and will screw your engine if you are not careful by allowing grit into the cylinder.

Any of the aftermarkets like the Hi Flo is what you should definitely install. Then you can consider converting your old filter by rejigging it to take proper foam designed to be oiled for air filters, then buy some proper filter oil. I did this but I'm still installing the normal replacement filter because in the end I couldn't be bothered.