LOUD Knocking.. I mean LOUD. Need help quick!

[insound]

I recently acquired a 94 SVX (FWD) and I was pretty tickled to have it. I was deeply heartbroken though when the tiny little knocking noise in the front end completely screwed me over.

Here's the story: I got an SVX from a friend of mine. It had a moderately-loud knocking noise coming from the front end. Everyone was telling me it was the axles, so I thought "no big deal, right?" I was horribly wrong.

I took off from a stop sign with a somewhat strong gun on the accelerator (don't think I put it pedal-to-the-metal). And after going about 2 feet, that little knock got LOUD. Now the car knocks faster with speed and bucks the car simultaneously.

I went to a local mechanic and had both front axles replaced, and that didn't do a thing. The mechanic then told me that it was my transmission. Needless to say, I was infuriated. It didn't really help when I found out that a new transmission would run me about $3600 either.

I then came here and started looking around for SVX owners that have had or seen a similar problem before. I found a single thread describing my problem and people were saying that it was the front end differential.

I'm still somewhat unsure on what the exact problem is, which is why I'm describing it to you guys. I'm desperate to find out what the problem is, because my dad wants me to sell it. I reeeeeally don't want to sell it. I love that car just judging from the tiny amount of time I've driven it. Plus, if I sell it, that means I have to get my '97 Eclipse fixed and drive it around .

So to summarize my questions:
-What is wrong with my car?
-How much is the part to fix it?
-Is it an easy part to put in with little mechanical experience?
-If not, how much would labor cost on estimate?
-What would be the cheapest thing to do?

Remember, it's a FWD model.