We've used Trixbox followed by PBX in a Flash (PIAF) for our smart PBX for years. PIAF uses any old retired Windows doorstop as your PBX and can automatically record calls to/from some or all extensions or call groups, with recording also able to be started or stopped using * hotkeys on the phone. So you could turn on/off recording around collection of a credit card number. This is a manual process but effectively it's free, except that PIAF recently moved from free Asterisk to commercial 3CX for its backend that seems not to have this level of flexibility. I'm told IncrediblePBX is the free successor to PIAF but I never tried it.

If you have VOIP lines you don't need any other hardware apart from the pbx (and even that can be outsourced to commercial providers for cheap prices) or if you have copper landlines there's lots of FXO / Dahdi hardware out there. E.g. 4-line pci cards to slot into your PBX are around $50-60 on Ebay or you can get standalone SIP devices for a little more.