Having an arranger gives you the best of all worlds IMO. You can have a synth and a backing band. You can play with both hands with the arranger.

An arranger gives you the ability to practice with drums/rythms and a lot of flexibilities. The CASIO WK3200 is discussed a lot on this board and lots of pros here gave it much praise. The $300 price tag is not hurting it. Plus it has 76 keys ! And it is a full synthesizer in which you can change the sounds and you can even download new sounds from the net.

If you're not familiar with synth or arranger, this keyboard will give you a good intro without spending a lot of money and you can still sound like a pro ! You can buy this at Walmart/Costco that had 30 days return and see if you like it. Little risk