Got the boards.
I got 3 with 19mm because I read here, on other threads, that it is the "safe" choice. I could go with MDO but from what I understood, I need to know what I'm doing regarding cutting it and building a structure to support it. That is definately not the case!

I think 19mm MDF is more forgiving as it stays in place better and it is easier to cut and do shapes.
Also, for the t-molding, if I'm able to get it, I read that 19mm is the standard size or, at least, the most used. I don't have a router so I don't think I will be able to use it. I'll try to come up with a solution - I assume there are materials similar to t-molding that you can just glue or even nail to the border of the boards. Not as cool, sure, but at least it would protect the edges of the cade.
So the 19mm are for the sides of the arcade and the floor, if I get the desktop I spoke off before. If I go with the PI, it doesn't make much of a difference being the 10mm or 19mm, although I think I would benefit more, structure wise, from the 19mm floor.
The 10mm are for the bottom of the top of the arcade (below the marquee) - I'll try to get a drawing here later on.
The 3mm is for whatever may be necessary. It was around 2€ (3$) so I thought I should get it - I had a ride that helped me out so I needed to get all wood NOW or else I would need to order a home delivery and that is way too expensive.
Looking good! Falling back on schedule, though.
I'm gonna get the speakers tomorrow (6$) and the wood was around 61€ (roughly 65$)
Money so farMonitor: 20€ (22$)
Speakers: (still to be delivered) 5€ (6$)
Wood: 61€ (65$)
PC/PI: To be defined
Controllers (plus IPAC): To be defined
All: 86€ (92$)
I'm counting with 100€ (107$) for Ipac, buttons and joystick - from ultimarc. I'm from Europe, so ports shouldn't be that expensive. The 100€ doesn't take that into account, maybe 10€ more?
I was aiming for 200€ (214$) and it worries me that I will probably go over it - I hope that not by much, can't really worry about that now and need to continue the project.
Other stuff - configuring the PIIn case I can't get my hands on the desktop, I will use a PI as discussed before. I started to install Raspbian and Retropie and trying to get that to work. Seems pretty cool - I'm having some issues with the retropie freezing after a few minutes of activity, even in just the menus but I didn't read much about what may be the problem so hopefuly it is a matter of configuration.
As always, thanks for reading!