That being the case then a decent machine will be worthwhile.
Do you know what codecs were used to record the tapes? Also do you know what machines they were recorded on?
Due to the very narrow tape and slow speed even very small Azimuth error causes massive HF loss.
Studios often would record and should have done a 10 KHz signal to align the playback machine to that recorder.
Now Dolby B transfers very well between machines. Dolby C less well, and using the same type of machine helps.
DBX 2 transfers between machines poorly as a rule, with nasty pumping often occurring.
The type of tape is important as ferric, chrome and metal tapes all require different playback equalization to play correctly. So you need to know a machine you purchase can play the tapes you have in terms of formulation and codec.
I would definitely purchase a three head machine. Absolutely avoid reversing decks. Also avoid dual well machines.
I would look for pro machines from NAK, TEAC, TASCAM and Revox as first choices. Yamaha also had some good three head machines.
You must make sure the machine has the codec the tapes were encoded with or results will be beyond redemption.
If there are tapes that you highly value, I can archive them for you. I have a pro NAK and TEAC machine. I have Dolby B, C and DBX 2 for cassettes. I also have the equipment to keep the gear optimal.
I can record it to WaveLAB 9 pro via my RME Fireface 802. I can make you Wav. files to send to you, or master to CD or DVD-A. I have a lot of facility here.
My latest DAW.
Are there any reel to reel masters of the studio sessions?
Finally how old are the tapes? Some tapes develop failure of the binder. They bind and shed which fouls the heads and can not be played.
I have a system to restore these to get one play to archive. That usually works but not always.
You can PM if you need any help with this. You can get good fidelity from cassette but it is not easy.