Since the question revolves around money I thoroughly agree with Bill. The 123 is by far the cheapest to maintain. Included in the benefits are that it is the easiest to DIY.
There was an era change with the 201/124 models. All cars since then are a quantum leap more expensive to maintain. Most of the differences are with the A/C but all the electronics and creature features make the new era cars way more expensive and technical.
Bosch Master, ASE Master, L1
33 years MB technician