Ok, I searched the forum and I could not find any math on this. I've seen various numbers being thrown out for budget for spell haste:

On shadowpriest.com, someone posts that the spell haste budget is .835 (shadowpriest.com :: View topic - the patch and spell haste). They do not post their math or what items they used to make this comparison.

I found a blog that claims that the spell haste budget is .934 (Passive Haste studies.). They are comparing a healing bracer versus a dps bracer, and the math looks ok...

I thought it might be cleaner to compare two healing items. I took the [Swiftheal Mantle] and the [Amice of Brilliant Light[/item]. I liked these two items because they both use the same slot, they are of the same iLevel and same material, have the same armor and +healing. The only differences are:

The Amice has
+17 Stam
+11 Int
+9 Spirit
-27 Spell Haste

We can then calculate spell haste if we know the correct weights of those other three stats.

17s + 11i + 9t = 27h

Calculating for spell haste h, where s is the weight of stam, i is the weight of int, and t is the wight of spirit. According to Formulas:Item values - WoWWiki - Your guide to the World of Warcraft, the Spirit and Int are both equal to 1.000 and Stam is equal to .667 on a BC item.

From this, I get that h = 1.16!

So, either my math is way off here, the wowwiki budget is off, or there is something really weird going on with the spell haste budget.

I thought I'd try two different items, so i picked [Swiftheal Wraps] and [Wristbands of Divine Influence] and I found that the wristbands have:
+1 Int
+29 Spirit
+2 +healing
-28 Haste

So our formula is:

1i + 28t +2l = 28h

Calculating for spell haste h where i is int weight, t is spirit weight and l is +healing weight. According to wowwiki again, spirit and int are 1 and +healing is .455, we get that h = 1.06.

While these numbers are a little closer, both are pretty far off from the numbers I found on shadowpriest and elsewhere. Is there a more official crunch than this? Is it possible that spell haste has a different budget on healing items than dps items?

What you failed to read on the wowwiki page was that the itemization budget is not simple addition. You must take each stat times its weight to a power of 1.7095, add that up, and take the sum to the 1/1.7095 power. From here, there are various modifications to arrive at item level.

That said, stated item level and calculated item level don't always agree. Some items are underbudget.

Conventional wisdom (again, from the page you looked up int and spirit weights) is that all ratings have a weight of 1.