I guess there are three schools of thought on getting a spouse started:
#1 - Buy a really entry level (low cost) rod with the cheapest reel possible to see if the spouse likes to fly fish before you spend any significant amount of $$.
Pros: Avoid spending a lot of money on a rod/reel that may not get used, or not get used much.
Cons: If you get the spouse low quality gear their initial learning curve may be more difficult/longer, and they may not enjoy fly fishing (possibly dropping sport)?
Note: If spouse does not like fly fishing, you can always sell the gear on eBay or Craigslist.
#2 - Buy the spouse a decent Upper-Entry-level to Mid-level rod/reel (range of TFO or Reddington to Scott A-3), hold $$ cost down to a reasonable level.
Pros: Providing better gear may make success of spouse enjoying fly fishing higher since they will have good gear to get started. Also you can avoid having to buy an upgrade in a very short timeframe, mid-level gear may be all they need for years to come.
Cons: Have to lay out more $$ to get started
Note: If your spouse does not like fly fishing you can keep the rod/reel as a backup - do you want to use the low-cost gear, or decent mid-level gear?
Personally I subscribe to the 2nd school of thought - bought my wife a TFO Pro 8'6" 5wt with an Orvis Battenkill Barstock reel and some decent fly line. Not expensive gear, but not cheap stuff either. She attended a 2-day fly fishing school, and has enjoyed fly fishing and catching trout for several years - still using the same original gear. If you arrange for casting lessons along with decent gear, you have the best chance of having a spouse or child learn to enjoy the sport!
#3 - Buy the best gear available
Pros: If she does not like fly fishing - YOU get to use the gear!
Cons: $$ Ouch! $$
Note - More power to those who want/need/can afford really expensive gear, keep buying as we all benefit from a strong fly fishing industry and the research and development that goes into supporting high-end gear.
Side note: I will not be buying $600-$800 rods or $300-$500 reels to outfit my spouse - at least not until I win the lottery and I can afford that kind of gear for ME!
2nd sidenote: Based on my knowledge of ME - I absolutely did NOT try to teach my wife how to fly fish (obviously since I am still married!).