As stated earlier in the thread, it may be a good idea to get the electrical utility company to come out and check if everything is ok on their end. Shouldn’t be any charge for that.
Voltage shouldn’t fluctuate much in the home. If it does, then there’s usually a burnt up connection somewhere.
My usual charge for replacing a 100A service panel is about $1500, maybe $2000 if it’s a 200A service or I need to replace the meter and mast as well. It’s often a full days worth of work.
BTW, does this thread qualify for oldest resurrection? 11 years is quite the gap.