Alternative to REF200 Current Source
A link to a data sheet and some idea of your key target parameters is always useful when asking questions such as this. It saves N people looking up the same data and ensures we are looking at what you really want to replace and not something only similar.
 REF200 datasheet 

I tried searching Digikey for "current source" and ordering results by price.

This seems much cheaper than the TI part and at 1st glance has similar spec - plus its MUCH more flexible I think.
 If this is no good then working up Dikgikey offerings in ascending price order or specing tightly and sorting by price shoud produce something suitable.

NXP pssi12021.  

$us0.66/1. $us0.26/1000
 15 uA TO 50 mA programmable
 0.5%
 0.15%/K &lt;- much worse than yours :-( 
 Vsupply &lt;= 75V !!!  



ADDED

The 0.25% spec seems to leave only the REF200 and this IC from Digikey.
 The PSIxxx has a far worse temperature spec (0.15%/K = 1500 ppm compared to 10 ppm for REF 200. 

Temperature change of 1K is about 0.3% absolute so temperature stability is about 50% of temperature reading per K. Sounds wrong. The ratio of 1500ppm/10ppm = 150 :1./ The PSixxx is specified over a -55C to +150C range (!!!) so it's is just possible [tm] albeit unlikely that 0.15% is change over whole range. Unlikely! :-).

Roll your own should be cheaper than TI and as good or better, but more work.
 How many do you need, what do you want to pay, what will you pay me ? :-)