Looking for cheaper alternatives/solutions (then going to the dealer)

a) We can no longer down shift to 2nd or 1st gear. When we go to 3rd gear and press the down shift button on the shifter, nothing happens. Dealer says it will cost $100 / hr for inspection to see what's going on.

b) When we fill up our gas tank, the fuel guage still says empty. Then suddenly after a quarter tank, the fuel guage seems to work fine. Could this be a problem with the sender?

c) When we turn, we constantly get noises from the steering. its like a clunking noise. Dealer claims there is no issue, but when we drive and we make turns, it almost feels the car isn't making a smooth turn.

d) Our horn doesn't work correctly. When you honk, it's not very clear...it sounds like you are pushing air and you can barely hear the horn...can this be easily replaced or fixed?

Any input on these would greatly be appreciated.

a) Are you talking about manually shifting the car or the car shifting itself, because if it's struggling shifting itself it could need to be rebuilt or a transmission sensor could be bad. Is it throwing any service engine soon or service vehicle soon codes?
b.) Sounds like an old GM fuel system problem, it could be the sender, which I believe is attached to the fuel pump so the pump would have to be replaced.
c.) It sounds like something with the suspension/steering system is going bad. It could be your rack.
d.) A horn would be very easy to replace I would imagine because it's right there and doesn't seem like it would be too hard to deal with.

I have a lot of the same questions as green03malibu, for clarification:
a) When you say "press the down shift button", are you trying to move it from 3 to 2, or are you just leaving it in D and stepping on it?
b) Sometimes you can pull the pump/sender unit and replace just the sender with an aftermarket one, but you need to determine that it's the cause. You have a gauge that takes that signal but also needs the correct voltage from the instrument cluster voltage regulator. Make sure of what is actually at fault. Your description lends itself well to looking at the sender first.
c) Does the clunk happen as the car is moving or can it happen while standing? If it happens only when moving, one thing to check is your CV joints (constant velocity). They are like a U-joint for front-drive cars. If a boot is damaged and has allowed dirt to get in then you may need to replace the CV joint. The noise it will make is a continuous clicking as you move forward with the wheels turned, but will diminish as you straighten them out, usually going away once completely straight.
d) Find your horns, unplug them, and use a jumper cable to put +12V to one and then the other. If they still don't sound right, replace. If they do, check your relay first and then your fuse.