What is your brand and model of computer?
In which part of the world do you live?
This is a difficult question for an accurate answer online...
A top flight, repair consultant might fix it all in an hour, but the cost per hour would be high... from $55 to $135 per hour, plus parts. Some have a $45 minimum. Some have a $150 minimum.
You might find a person who works for $35 and hour, but he might take a day and a half
Your problem could take hours to decipher... or be found in seconds.
It is important to talk to as many technicians as possible... in person, if you can find a person with the time to talk. You want to know the breadth and depth of their experience. A good technician has thousands of hours invested in training courses, reading materials, parts, and especially, software. He or she might have $3500 to $10,000 invested in certifications. Then there is health insurance, shop rent, electricity... you know the drill.
But a enthusiastic guru with little formal training might be just the guy. You just never know until you ask around.
When we know a little more about your setup, we can give a better guess, but it will be merely a guess.
The best repair person I know is an autistic fellow who is 19 or 20, and works a regular job of 40 hours a week. He can fix everything, but cannot figger out what to charge, or even talk to you coherently, but he is better than most techs will ever be. He works in a sheltered environment where benevolent managers assure he has great work space, and pay that meets with his value.
If it requires memory, perhaps $50 to $100 for memory, and $35 for diagnostics. If it is a video card, it could be $75 to $75, plus $65 labor.
You need to find out what the standard may be in your area.