For just bashing and having fun on a budget, I vote for Ni-MH. I started out using 1500 mAh Ni-Cd batteries and had a blast. You can get 2000-3500 mAh Ni-MH batteries for $15-$30. Just get two or three and you should have a decent amount of runtime. A good peak charger can be had for $50 (give or take, depending on what features you want) that will charger your batteries in under an hour.

Don't ge me wrong. I love LiPo batteries. I use them in all my planes and I just bought one for my RC18. However, I have spent more than I care to admit, and Ni-MH work just fine for bashing. Just the other day I pulled a couple 3000 mAh Ni-MH batteries out of the closet which had been sitting since last year. Charged them up and popped one in my 1/10 buggy and had a blast. I think the batteries cost me around $25 dollars each a couple years ago might be even cheaper now.

LiPo is the way to go if you are looking for ultimate power and long runtime. However, with modest motors I can get 10 minutes+ easily with my batteries. So you know what I mean by modest (people's opinion of modest varies), I clocked my 1/10 buggy at 23 mph with a 1500 mAh Ni-Cd. Not super fast, but I am geared for torque, so it gets there fast. In my yard I can't resonably go faster than that anyway.

Now that I said all that, I have a LiPo and brushless in my RC18B. It is faster than my 1/10 buggy and gets there almost instantly. So...LiPo can be very fun .