Bought a pristine SPCH-1001 audiophile PS1 about a year ago with controller and a few games, including Namco light gun, for $45 shipped, with the goal of PSIO modding from then. Only problem has been availability. These parallel port PS1's are all over eBay for $25, and you can get then with broken CD drives for barely more than the cost of shipping. Popped open my PS1 and found I had the PU-8 board. Followed the directions and the switch mod was pretty easy. The hardest part was just the time it took to get the fiberglass pen to scrape down enough enamel in the ground point so my solder would properly bond. Little kapton tape to mask off the nearby vias and had no trouble here. Really just a very simple install - always double (triple) check each step of which trace you're cutting or where you're soldering, use plenty of flux and stick with quality solder. Multimeter check continuity on the trace cuts and nearby traces, and also while soldering each wire. I used a fine tip on a Weller digital at 525*F with Kester solder and had no problem with the small solder spots.

My only complaint from the design is the PCB pads require having wires crossing over each other. If I designed this, I'd arrange the pcb pads in an order that doesn't require external wires to cross so a nice and tiny ribbon cable could be used, a la Lord Voultar's mods. I may even redesign the pcb to do this since they've released their schematic and are fine with people using it to make boards.
Ripped a few discs, used the PSIO software to merge bin files and generate CU2 files, then created some MULTIDISC.LST files, and got the 80x84 .bmp images.
Then found out I needed a firmware & FPGA update, so I went through that process too.. again, well-designed. PS1 works from CD as normal, but also plays perfectly from the PSIO. XA audio was fixed in the early December firmware update. When I install this in a shelf, I'm probably going to put some quiet active cooling blowing on the PSIO. Even though it may be designed to handle the heat, I'd like it to last forever.

..and now my Dreamcast awaits the DCIO, which I'll likely purchase when available.
As for the cost.. mint condition parallel port PS1 with controller and cords = $35 shipped on Ebay all day, even less with a broken CD player that you won't need to ever use. PSIO = $131 shipped from Stone Age Gamer. 128GB SDXC card $33 shipped on Amazon. There aren't too many other consoles where you can get the whole system with flash drive storage for under $200. The SD2SNES is just about that much without a flash card or SNES. Not having spinning discs and support for 512GB+ SDXC cards is huge on a system like this. Compared to the $80-196 for other flash based console kits, I don't think the PSIO is expensive at all.