I've tried a few substitutes over the years and have found that exercise and fish oil are enormously helpful. But if you need a little more of a boost SAMe is excellent but pricey. I recently found an affordable brand called Jarrow. It provides 200mg per tablet. There are 60 tablets per box. It comes to about $17 dollars a mo. if you only take 1 tab a day. Some people need more but I found that 400 a day caused me to be nauseous.
Also, St. John's Wort ? helps some people but for me it brought on tinnitus (ringing in the ears).