It depends on your "market" whether ABC is the "best" format. It's popular here, because people have learned to work with it; but that may not be true for others. The Library of Congress doesn't offer it, do they?

Transcribing from audio requires that you have someone who can do it, and is willing to do it at a price you can afford. (Free would be best?) It's extremely time consuming. You also need to make sure that your "transcriber(s)" can be trusted to distinguish what's tune and what's embellishment; and a consistent "policy" regarding whether or not to include embellishments, counter-points, alternate (harmony) lines, etc.

Even if everything you're working with is by known composers/performers that you're sure are willing to have you use the tunes, or is "accepted" as being "trad" not subject to copyright, you should have someone willing and able to do at least a surface level look at potential copyright claims. There can be lots of surprises in this area.

For your print copies, the ONLY acceptable format is standard music notation on staves with notes, unless you have prior agreement from your users on another format.

Since there are no universal notation program formats, for web posting this probably means pdf or graphic files.

For a "low budget" alternative, for some kinds of music, you could perhaps print lyric-only books (most tunes don't have accepted lyrics) accompanied by a disk of mid files, or have midis on the web that people could get separately; but I've found people "resistant" to making the effort to get stuff from two separate places.

With very few exceptions, any program you choose to print from can (almost automatically) generate midi files from which people can play back the tune. Almost any music notation program your "customers" are likely to have can regenerate a "score" from the midi, although it may or may not look like your original one.

The midi can also be used to generate ABC notations of the tunes, by those who have the right program(s), again with the caveat that results may vary.

If you're going to print the tunes, unless you make an extremely unfortunate choice of scoring program, you'll "automatically" have .mid files for each tune. It's just a matter of doing the saves as midi for each tune from the scoring program.

The files generated by the scoring program for printing probably can only be used by those who have the same program. There are a few programs that can read the formats generated by a few other programs, but the programs with this capability tend to be expensive and require "learning" by each user. Posting these files on a website will be of little use to anyone, unless you can make a "reader" program available to those who may want to download them, and that your clients can use to print from the files.

If you want people to be able to print the music from the website, either a pdf or a graphic of each page should be your choice of what to post. Either jpg or gif are good compact graphic files for this use, and most users will have a program that can print them. Anyone can download the free pdf reader, so you can be assured that all users can print from pdf files, but the files are a lot larger.

Either format, jpg or pdf, can be made from scans of the print copy, although other methods may be more efficient if someone has the programs needed.

If those who will be downloading want another format, such as ABC, it's fairly easy to generate ABC files from the .mid ones. I would suggest that if you choose to post ABC versions it should be in addition to posting printable and midi versions.

If you want people to be able to download "something to listen to" then probably midi is your best bet. Almost all people with a PC or Mac or 'Nix can play midi files. MIDI files also can be converted to printable scores by most notation programs, so those who have a program may want to use them in that way.

As to costs: Re-scoring the 415 odd tunes in a local "Session Book," and adding about 260 "variations" that I knew were popular elsewhere, to get them all in consistent and usable format, took me about 2,500 hours. [A standard metric for labor cost estimating in the US is that one "man year" is 2,088 manhours. At a "cheap clerical" rate of $15/hour, I "donated" $37,500 to this effort.] I had "printed" scores to work from, although some were marginally legible and quite a few were unplayable and required corrections.

Printing one copy of the resulting book on my laser printer cost me about $21 (US), and would have been nearly double that (paper and ink) on an inkjet. A local printer would copy the master print for about $18/copy in minimum quantity of 20 copies. I provided a floppy disk of all the midis for the tunes, which was a minimal cost to make. Offered to the local tribe at $20 each, it took me about 5 years to "break even" on the printing cost, so that book is no longer in print.

It took about another 300 hours to convert the whole thing to a Word file on CD, with embedded jpg graphics, and with linked index and table of contents so that you could click on the tune name and go to the printable tune, or click on the tune number to play the midi. I also included the same "document" as pdf on the disk, along with a separate jpg and a midi file of each tune. I haven't advertised the CD, but haven't found any interest in it (at $10 per copy I've sold 2 in 3 years, but that was an accident.) I don't really consider the CD a "finished" product.

Note that this was a massive collection, and a smaller project may have significantly different "market dynamics" and costs.

John