Re the different prices, what Bongo said above. Many players can get by just fine with a 10-buck string set, even, if their skin chemistry agrees with it (sometimes, a product just doesn't last on you - it happens). Some sets cost fifty bucks because they're imported (but the tone makes it worth it for you), some are coated, some are more time/component/labour-intensive.
Re differences, especially in tone - in a nutshell:
- roundwounds (the undisputed standard for at least four decades) are less expensive, as a tendency less durable, but wider-range (more sustain, more mids and highs). Their treble response sometimes needs to be reined in, by cutting highs at the amp, or simply with the tone knob at the bass. They're rougher to the touch, and finger-noisier (all the fretting hand against string squeaks get amplified, unless you EQ them out, as said). Of these, the clear majority are nickel-plated steel (NPS for brevity); compared to them, stainless steel are more trebly, whereas pure nickel wound strings (Fender 7150; GHS Balanced Nickel; Thomastik-Infeld Jazz Rounds) are warmer-sounding, and less common;
- example of coated rounds are the Elixir brand, DR colored strings, D'Addario XT, Ibanez. They sound like rounds, essentially (with a little less zing and finger noise), but last longer;
- modified rounds (pressurewounds, as made by GHS; groundwounds like D'Addario Half Rounds and GHS Brite Flats) are smoother to the touch than pure rounds, less squeaky, less trebly, still very versatile;
- nylon tapewounds have subdued highs, but can be very lively (some of the sets that LaBella makes are transparent in appearance, and called White Nylon, and the brightest out there in terms of tone, too; the rest, including some others by the same company, are black in colour, and darker in tone, with Fender and D'Addario being still classifiable as "bright" to an extent, and Rotosound Tru Bass 88 as "thumpy". Tapes potentially last a long time;
- flatwounds also last years, as long as you still like their tone by then, and come in many flavours. Most start out a little clangy (for most of them this goes away with some breaking-in) but the balance of bass-to-mid/treble varies:
- Ernie Ball Slinky Flatwounds (colloquially "Cobalt Flats") are
bright, and comparable to worn-in roundwounds; D'Addario Chromes are also pretty bright (in time, again depending on hand chemistry, they get darker);
- Rotosound Jazz Bass 77, Fender 9050, Thomastik-Infeld Jazz Flats (often referred to as "TI flats") are different from one another but make up a loose category of
midrangy flats;
- Ernie Ball steel flatwounds (aka "Group" flats), Dunlop flats, Sadowsky flats, Optima flats are often described as
in-between the brightest and the darkest bunch (there may be crosstalk or differences in attribution within this category and the previous);
- La Bella Deep Talkin' Flats, DR Legend, GHS Precision, Pyramid Gold (and others) fall in the thumpy,
traditional (they were an important component of the classic electric bass guitar tones of the '60s), dark camp.
just fine.
Generally speaking, flats slot very well in band mixes, but they don't lend themselves to "cutting through" per se, and may sometimes have trouble with note definition unless some care is taken in EQing them (mid boost, bass cut).
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For classic blues with some slap thrown in (and some judicious use of the tone knob), I'd conside r
- pure nickel roundwounds;
- pressurewounds or groundwounds;
- black nylon tapewounds;
- bright flatwounds
as outlined above. Another's mileage/take may vary.
