I use a Yamaha AW16G standalone DAW. It runs about $900 new now but you can get them on eBay for around $700.
I record my Technics digital piano into the 16G all the time. 1/4" stereo out of the Technics into two separate 16G 1/4" inputs. You can add all kinds of effects that really bring out the piano.
Might be a tad more than you wanted to spend but it's what I use and I couldn't be happier. I think Korg and Tascam make some really cheap DAW's that get really great reviews.
If you want to learn everything there is to know about the 16G you can go to
www.aw16g.com. It's a BBS not unlike this one only dedicated to the AW16G. It's an amazing resource.
Good luck.
Tommy