Hi Earth Bro,
Just my 2 cents for ya.
Been to few LFS last time for some tank quotation on a 6ft x 2ft x 2.5ft tank.
It was about $9** + for main tank and sump. So for your 4 ft, I will estimate around $7** +/- for main tank and sump. Not to forget a BecKett, depending what brand, say around $8** inclusive of pump.
All in all, you probably spend another $1700, you can have 1 good system. Oops , what about the old tank??? Try to call Town Council from your area and get it removed free of charge.
Sigh...I know $1700 is not a small sum to many of us. But sometimes, short pain better than long pain la.
Just my suggestion...
dsam