Well, it partly depends on what you consider a monitor. If you're talking about the really small monitors with a 4-5 inch mid-woofer, then 40Hz is really not an option. If you get up to 6-8 inch woofers you might find something that goes there but it will of course be in a larger cabinet. You do need to be a little more careful in making a selection because integrating a larger woofer like that with a tweeter requires a good tweeter that can cross lower since mid-woofers of that size have a little harder time reaching up into the upper midrange cleanly.
As far as the instrument itself, the 'typical' bass has a lowest frequency of about 42Hz (open E). There are of course exceptions with specific instruments that have lower fundamentals. Much of the sound is harmonics though, so even if you can't get quite that low you may be satisfied with the sound.
One thought that comes to mind is the B&W 602's. They get down to about 50Hz and can be found for $600. The 603's got a rather nice write-up in Stereophile recently but of course only you can decide if they are your cup of tea.
You should definitely play with placement. In general, most speakers will gain bass by being placed on a bookshelf or close to a wall. Unfortunately, this increased bass is often somewhat peaky and can be a bit muddy. Depends to some degree on the speaker and the crossover design. In the "old" days, speakers were often designed without baffle step and so their frequency response actually dropped off quicker than "spec" if you moved them out into space. Manufacturers now do a better job of designing with the specific goal to be flatter in the bass region even in free space. Move them around until you get what you like.
As far as the instrument itself, the 'typical' bass has a lowest frequency of about 42Hz (open E). There are of course exceptions with specific instruments that have lower fundamentals. Much of the sound is harmonics though, so even if you can't get quite that low you may be satisfied with the sound.
One thought that comes to mind is the B&W 602's. They get down to about 50Hz and can be found for $600. The 603's got a rather nice write-up in Stereophile recently but of course only you can decide if they are your cup of tea.
You should definitely play with placement. In general, most speakers will gain bass by being placed on a bookshelf or close to a wall. Unfortunately, this increased bass is often somewhat peaky and can be a bit muddy. Depends to some degree on the speaker and the crossover design. In the "old" days, speakers were often designed without baffle step and so their frequency response actually dropped off quicker than "spec" if you moved them out into space. Manufacturers now do a better job of designing with the specific goal to be flatter in the bass region even in free space. Move them around until you get what you like.