lumber/screws/glue is probably 30-35% more expensive than most other countries, if not more.
Ouch. I guess you guys have more seacoast than forest though.
The big issue here is that 2000$ is probably about enough to get you ready to buy big-boy amp and subs that will get you very loud or enough to buy a decent head unit plus electrical upgrades to support the big amp and subs.
High output alternator in USA runs 500$ give or take you're going to need 600$ worth of additional battery to support 5K amp and you very probably want an aftermarket head unit (plus install kit) and at least a modest size 2 channel amp and some components or coaxials up front in your doors to keep up. So that's about 2000$
5000W amp (full bridge) will be 500$, two solid woofers that will handle that power will be 500-600$ each, box will probably be 200$ in materials, then you will want 300$ for cables (1/0 cable back to your battery bank and big amps will need multiple runs of 1/0 to their terminals), RCA cable, speaker cable, and battery terminals. Also about 2000$
I may even be under-estimating the cost of equipment and materials over in Europe but I'd say you'd want to plan to spend about 4000$ for a build that could put up around 150dB on the meter and be solid enough that you would be able to play for extended periods of time without worrying about premature failure because you had to cut corners.
As far as box building. If you have a power drill/screw gun, circular saw, and jigsaw you can do just about anything. Caulking gun should be 5$ and 10$ worth of construction adhesive goes a long way in making up for amateur uneven cuts. If you want to get pretty power sanding and a router is nice, but certainly not required. I've bought tools to build a box for about 100$ used at a pawn shop when I was on vacation one year so that I could build something simple to run in a competition. Wasn't pretty, but got loud. Anyway, yes you absolutely want to build it yourself and many manufacturers will have plans published on their website and you could probably even ask for help around here.
If you still want to proceed you may need to prioritize what you want first and start upgrading as you can, but you definitely do NOT want to buy a 5K or 8K amp and try to run it without electrical upgrades. It will break. Personally I'd start with decent head unit, 2 or 4 channel amp and some nice fronts. Get good wiring run to the back of the vehicle then possibly the subs and box and just buy a tiny amp for subs to keep you going until you can get your electrical upgrades right then add that + big amp.
