Hello, my name is XXXXX XXXXX I'm here to answer any of your electrical questions.
No, it is not safe. It is against code to not follow the manufacturers instructions anyway. A new circuit would need to be ran from your panel to your new range.
No the wire needs to start from the panel as a 8 gauge wire. It is not safe because a 10 gauge wire is only good for a 30 amp breaker. Your range probably requires a 50 amp breaker.
Wire is only rated for a certain amperage.
10 gauge is for 30-35 amps depending on the wiring method used.
When I mention 8 gauge and 50 amp breaker it also depends on the wiring method used. If it is romex #8 can only handle up 40Amps. If it is ran in flex, or conduit it can handle up to 50 Amps. As far as cost goes the best thing I can advise you to do is contact 3 different electrical contractors and get prices from each. The reason for this is prices vary from city to city. Even from company to company. There are a lot of things to take into consideration depending on what obstacles a electrician has to go through to accomplish what needs to be done.
If you want a really rough estimate. Anywhere from $500-$1000
It could even be as cheap as $300 depending on how far away your panel is. and what wiring method could be used.
What is the amperage of the old unit?
I need to know either the watts, or amps
Well # XXXXX is good for up to 35 amps as I mentioned earlier.
That would depend on the amperage of the unit.
Here is the problem. Like I said #10 is good for 30 to 35 amps depending on your wiring method. If it's romex 30 amps, if it's ran in pipe, or flex 35 amps. Say your method of wiring is romex and your appliance draws more than 30 amps, then you are in trouble and are causing a risk of fire. The breaker should be on a 30 amp breaker if you have romex. If you are going over 30 amps, the wire will melt and eventually short out causing the breaker to trip, or even start a fire. Without all the specific information that I am asking you for, there is no way for me to tell you if something is right or wrong. If your home is old, that may have been fine back then. But because you are going through with a new installation, you need to follow all the new guidelines. The manufacturer has a reason why it needs to be 8 gauge wire. I have provided you with all the information I can give you with the limited information that you have given me. Sometimes we have to give information that you don't want to hear, but it is what it is. Please rate my service, thank you for your time.