Topband: BC filters and inductance calculations

[N1BUG]

Two unrelated questions:

A recent improvement to my station has brought other issues to the 
forefront. I am going to need a serious filter to keep AM BC 
stations out of my preamp. I had been thinking bandpass filters, but 
none I am aware of roll off quickly enough below 1.8 MHz. I am now 
investigating high pass filters. The W3NQN filters sold by Array 
Solutions look very impressive. Is there anything else (maybe a 
little cheaper) anywhere near this or are these in a class by 
themselves? This will be a receive only application.

I am also looking for a better formula for calculating inductance of 
single layer air core coils. Although I have done well enough over 
the years with the "simplified formula" from ARRL Handbooks which 
gives a "close approximation" I now wish for something better. 
Ideally I would like something accurate for coils of any length to 
diameter ratio, including very short coils. A free downloadable or 
online calculator would be great, but a plain old formula is fine 
too. I have found several on the internet but which ones to trust? 
Any guidance would be appreciated.

Thanks, 73, & HNY!

Paul N1BUG