Yep.
DVI-I is actually comprised of both sets of wires. One for DVI-D, and one for VGA.
The VGA output is tapped off the DVI output and run through a DAC (Digital to Analog Converter). You require either:
1) VGA output, or
2) DVI-I output + VGA adapter, or
3) external DVI to VGA adapter (powered), or
4) DVI input
All of this requires new hardware at some stage, either the GPU, adapter or monitor.
Sorry, but that's unfortunately where you are at.
*My only advice really is to put back in the old card until you can afford a new or used monitor with at least a DVI input, though perhaps DP or HDMI as well to connect other devices.
(HDMI + an audio output of some point can allow a game console or similar device as well to share the monitor)
Update:
You can use the current monitor as a secondary monitor if you want later, but you'd still need to have it connected to your old card with the new card and new monitor connected together.