I revived a pair of diy enclosures of a very old project of mine, added some mods, calculated the costs for one enclosure to be included in my final calculation and ordered some midwoofers (already had multiple pairs of fullrange speakers. (TB w3-871, TB w3-315, Visaton FRS8-8, Visaton FRS8-4)
So that wasn't an issue to test which fitted best sound-wise)
Currently the costs for one speakers are: €130, see parts list for details
Speaker specs are:
Resistance: futile! (joking ;) it's 8ohm)
Power handling RMS: about 50W
Sensitivity: i think it's about 84DB SPL @1Watt/1Meter, i don't have the tools to measure it
Frequency response: 38-20000hz (portnoise might occur on very high volume)
If using less than 30W RMS, you can go lower (xmax won't be an issue then)
Nice project, especially as you are on a tight budget. Maybe a bit offtopic, but I'd love to hear a bit more about your subwoofer. Might form a nice addition to this!