Well i personally would go with an internal mod chip a Neo 4 or higher ( i dont recommend the Neo2.2 chips cause you need to do swap tricks for your games to work.)
The only bad thing about internal chips are that you are voiding your warrenty if you put on in.
and you have the: USBMOD / NEOKEY.
The good thing about these is that they are compatible with every model PS2 (US/EUR).
It slots nicely into the PS2 USB slot. You can now play your PSX and PS2 backups (compatible with All Titles including EA Sports Games that have been patched with the new EA Patches).
the down side is that the USBMOD requires a Game Shark 2 (US) or Action Replay 2 (Euro) to play your PS2 backups. PSX backups play without any need for either of these.
You still need to open up your PS2 but you are only required to solder 1 very easy link wire.
And thers the NEW PnP key Solderless Modchip.
the good thing about these are:
*No Soldering needed! just Plug and Play!
* Plays PS1, PS2 CD and DVD backups.
*Internal Mod-Chip built-in.
the down sides:
*Works only with V5 & V6 PS 2 main boards SCPH-3000xR (JAP/US/PAL ).
*The PnP Key requires a GameShark2(US) or Action Replay2(EURO/PAL) to play PS1/PS2 backups.
and for the prices it all depends on where you are going to by them.
i suggest
modchip.com
mod-chip.com
ozchips.com
ect
hope thats some help
cheers