Front end violently shaking??

I know there are many postings on here about this, but I wanted to see if mine was any differant. This morning I was driving my 2000 Tahoe Z71 4x4, Older body style. 97,000 miles down the highway. I hit about 65-70 and the steering wheel started to shake violently. I had to slow down and it stopped. I have noticed that it has been wanting to shake like that for a while. I could feel a gradual onslaught over time. It rides like a Cadliac as far as shocks go and likes to sway a bit going down the highway. The front end feels loose when hitting bumbs and the steering wheel will fly back and forth when doing so. Im not that great of a mechanic and have never done much more than brakes and tuneups. What should I look at and or consider?? Also would you happen to have an estimate as far as price for parts?? Also one more quick thing. When I accelerate from stop and sometimes when pulling my boat. I hear a sound coming from my rear end that sounds like a short tap of the horn when the load is transferred to the back. Any ideas?? Thanks guys.

Check all steerning parts. Look close at the idler arm.

i would start with a tire rotation and balance. With the front tires off the ground grab the tire at the three and nine o'clock positions and try to shake it back and forth. You shouldn't feel any play. Or, keep the tires on the ground and have someone saw the steering wheel back and forth without the engine running and look for play in all the joints. like taillight said, the idler arm and pitman arm are common areas for failure. If you replace parts, use MOOG replacement parts.