Need a shift solenoid replaced on 2005 ford taurus?

I have a 2005 ford taurus. Engine light is on and occasionally comes on the led screen saying check transmission. I had it checked out and was told the shift solenoid was going bad. Mechanic said he would let me know how much it would be and stuff. I ve already ordered the part and everything. My issue is that I m not hearing from the mechanic now and can t get in touch with any other mechanics. I called a shop and was told that replacing only that part would be a waste of time and that we should just go ahead and get a whole new transmission (is this just fishing for money on someone who doesnt know cars?) I was planning on getting a new car in a few months anyway so theres no way I m putting 1200 into this one (it was used, i only paid 2000, has not sentimental value or anything so just not worth it to me). How long will the car last without this part being replaced, how much would it run me to get that part replaced and if i do get it replaced, is it just gonna be having trouble again in a month).

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