I've recently been in the market for a digital piano myself and considered the Casio PX-3 among others but was put off by hearing of SO many people who've had problems with wobbly and clicking Casio keys after they've had it for a while. Not only on this model, but on a lot of them. Not saying they're all like that, but knowing my luck, I'd get one of them.
I ended up with a Yamaha DGX 640 - it's about the same price - and I prefer the feel of the Yamahas compared to equivalent Casios anyway. I also considered a Roland F110 - a bit more expensive - but couldn't find one to try live and most reports say the keys have too light a touch so ... meh.
I'm enjoying the DGX 640. The keys feel nice for the price and the sounds are pretty decent - well the best ones, anyway. There's so many sounds I'll probably never use. It's got a billion features I'll probably never get round to using either but at some point, they may prove useful.
It's not exactly lightweight but I don't intend to drag it about anyway and I got the optional 3-pedal board for it as it's intended primarily as a digital piano to continue my studies. I learned initially on an old acoustic but the keys on this are so much better. And the other "fun stuff" can wait till I'm at a loose end. It's also got their Y.E.S. (Yamaha Education Suite) built in so's you can isolate different tracks of a midi - say the right or left hand while you learn the other - and the score is played on it's computer screen and it goes at your tempo. Might be interesting to a beginner. Haven't used it myself yet so I can't really comment much.
I know there are far better digital pianos out there but for my budget, this was the best I auditioned. No regrets buying this DP. The keys feel nice and responsive and that was the main thing for me - that and the price. Some say the speakers are underpowered, I say that depends on what it's used for. In my house, they're more than loud enough at 3/4 volume max. Any louder and I'd have the police in! Besides, I've already got a 45w keyboard amp in case I feel the desire to play it somewhere bigger.
Can't think of what to recommend cheaper to be honest. But it's pretty important for a beginner to get a decent digital piano anyway or you'd end up playing all wrong. For instance, I tried out a semi-weighted keyboard and it was utterly impossible to play softly on it. Graded hammer action keys are a must unless you're an expert player and/or just want a synth or midi controller.
If you're worried about giving up, go for the "big" names like Roland, Yamaha, Casio, Korg, Kawai etc. because if you DO decide to sell it on, at least you'll get a decent price for it.
Good luck with whatever you get.
