Easiest speaker projects use just a single driver mounted to a simple partial sheet of plywood. With the right drivers (high Qts) and placement away from the back walls these open baffle (OB) designs are extremely dynamic with very realistic imaging. Bass output is the challenge, but larger baffles, the right drivers, and especially digital EQ helps.
Cheapest drivers I'd recommend: Fostex FE127E ($75/pair, 92 dB/w/m, 8 ohms, 15 watts max, 80 - 20,000 Hz).
Best reasonably priced drivers by far: Visaton B200 ($250/pair, 97 dB/w/m, 6 ohms, 100 watts max, 40 - 20,000 Hz).
BTW, good digital EQ is available for $300.
Mount the drivers slightly offset from top and side baffle edges. Experiment with different baffle sizes using cheap materials.
The benefits of single drivers are many (direct "active" connection to the amp, point source imaging, no crossover distortions, no change in voicing at crossover from different drivers, simplest possible design).
So for $300 - 600 (+/- EQ for more bass) with the B200 drivers you could have a very efficient, organic sounding, idealistic pair of speakers. Or get a good taste for OB for under $100.