Mountain Biking - To trade or not to trade...

Hi guys. I'm in a bit of a dilemma here so I'd really appreciate some input.

I have three bikes right now - two not so great ones that I never use, and one KHS FXT Trail in excellent condition. (For those of you who don’t know off the top of your head, the KHS is a poor quality full suspension bike.) I use the KHS the most.
I want to get a better quality bike, but don’t want to spend too much money now (say, on a good FS). So, I’m looking into trading in all three bikes for a Specialized Hardrock. I’m sure it won’t be a straight trade, and that I’ll have to pay some extra cash on top of that. Does this sound like a good idea?

One more thing, I messed up my tailbone a few years back cause of a really bad landing on a hardtail. That’s when I switched to the KHS. Maybe getting the Hardrock would be kinda painful for me? I haven’t ridden a hardtail in a while and forget if they are a really rough ride on trails or not..

A little help here? Thanks

what are the two "not so great" bikes??

Infinity Spider and Infinity something else..heh that one used to be my brother's but he gave it to me and I never used it so I forget what model it is.

oh Infinity Incline

Hardrock would be kinda painful for me?

A little help here? Thanks
That is a question only you can answer. You might aswell keep your KHS's as you won't get anything much for them. They also may come in handy as loaners & or thrash bikes or something.

Would a Hardrock be good for wheelies and that? Roughly how big a drop do you think it could withstand?

Would a Hardrock be good for wheelies and that?
yep

Roughly how big a drop do you think it could withstand?
How big do you wanna go, 10,20, 30ft?

What, It wouldn't take 30 would it? 10 would be my max for now I guess, but...

What would a fair price be if I was to buy a basic Hardrock from my lbs? (pls tell me if you're talking in Canadian or US dollars thx)

You will most likely pay the MSRP of $390 USD . . . unless you are lucky enough to find a last-year's model in your size (unlikely now). Bike shops for the most part do not discount as a matter of routine like other retailers.

What is the difference between the regualar ones and the women's models? Is it really necessary? The shape of the frame is pretty different..that wouldn't make it any weaker would it?

Strength should not suffer. Design is very different to lower the standover significantly. If you have very 'female' proportions (longer legs/shorter torso) you may find the women's-specific design more suited to you. They tend to have a slightly shorter top tube length for the size of frame. Only way to know is to try both in person.

EDIT=Case in point: Regular HR Sport in 17" has a 590mm effective TT length; women's model is 575mm.