If you can give me a few more details, perhaps I can help.
Can you tell me what your signal source? What sort of source impedance does it have, does it have an excitation source that can it be modulated, can it be shorted out on a regular interval to re-zero, and what bandwidth does it operate over.
You mentioned difficulties with cable. Are you have difficulties due to triboelectric effects? You also mentioned difficulties with strong fields. Are these magnetic, electric, or traveling? What sort of frequencies.
As for 1/f, one must remember that as the frequency decreases, the available bandwidth becomes less (.1Hz is ALL the bandwidth from DC to .1Hz). So, There isn't an infinite event. However, it does look more and more like drift as you go lower in frequency. The ability to turn off, or short out, the source gives you an opportunity to zero out the drift between repetitive test cycles.
Generally, the processing circuitry isn't very expensive - though the first stage amp may proved demanding. It usually costs a couple of hundred dollars for a custom PCB and a few tens of dollars for associated components.