[FrankHudson]

I've used BIAB and the Trio pedal. They both use similar tech (Digitech licensed BIAB elements for the Trio). As with many "I'll magically figure out what you're doing" things, it may guess oddly about what to supply for bass lines. Sometimes those odd choices can be inspirational, sometime you'll need to "teach" it differently, or ask it to try again. Though I've used tracks from them in recordings, I generally don't. I do think they are both great tools though for practice and learning to play through changes.

For guitar players there's a lot to be said for just getting a bass, which is what I did. How soon can you start playing acceptable simple lines? Depends, but some guitarists with good time feel can be doing it very quickly. How soon will you become a great bass player? That's not assured, but even though it's a cliché from bass-only players of the "guitarist who thinks they are a bass player" some great bass players started off on guitar: Paul McCartney has already been mentioned, and in another thread I'm reminded of the legendary session bassist Carol Kaye.

A lot of great electric bass on recordings is "DI", meaning no amp was used. I like the DI options offered in Logic Pro X (and I think they're also in the free Garageband) for a lot of bass tracks, so you don't need anything that your DAW may not have like a stand-alone bass amp or extra-cost amp modeling software.

I have one of those Squier Bass VI models. I'll double what Steve said upthread. Some use it with appropriate strings as baritone guitar (tuned B to B usually), but I have it at E to E (one octave down). Bari guitar players can, and do, chord all six strings--though what voicings to use is a matter of art/taste. Typically bass lines are played as single notes and double stops on a regular bass or the Bass VI, and tuned E to E, the Bass VI just gives you an additional upper register over a conventional bass. Just as Steve said in his post, I, as someone who writes bowed string parts for my stuff, I think of it as an instrument with an additional cello or viola range. Or you could think of it as Leo Fender's take on the viola da gamba.

One drawback: the low E string is a bit tough to get good intonation set on the Squier Bass VI.

There are other low and moderate priced electric basses out there. My teenager used a Ibanez TMB100, which for under $200 is a valid instrument with very powerful active circuit pickups (teenager into late 20th century indie/punk, so this suited them fine).

Not as inexpensive, but I'm a huge fan of the Epiphone Jack Casaday bass. The complete opposite of the Hofner Beatle-bass copies Steve pointed out: not compact and not light, but actually designed with significant input from it's legendary name-sake. Sounds great, and sits well with acoustic guitar as one might expect from the Hot Tuna connection.

If you have little space and would like to fake more of a standup bass sound, the various piezo pickup uke basses around are an option. Super short scale and easy on the fingers I think they are great deal of fun. Once again you aren't going to chord them so much as pluck single notes and double stops. The cheap ones aren't built as lifetime instruments, but they sound all right when recorded.