Welcome!
If you're looking into a 2.1 system you'll need electronics that have can accommodate an extra low voltage output. Suggest monitors (versus floor standing loudspeakers) and either a sealed subwoofer (for music) or ported (limited to A/V special effects). Monitors wouldn't duplicate the bass a subwoofer produces, cheaper to buy, and easier to move/sell on.
Prices for monitors can range from $100 to $10,000. The best subwoofer system uses 4 subwoofers to reduce inherent in-room bass peaks/dips, so your first sub should go relatively deep but need not be extremely powerful. My first 2.1 system was used primarily for music and consisted of Ascend Acoustics CBM-170 monitors with a Hsu VTF Mk2 subwoofer ($830 total) and I still have the CBM-170's.
