First decide what kind of backpacking you want to do. If your goal is "light and fast" and long thru-routes then spending a lot on reducing the weight of your pack is justified. If on the other hand, you are more into a few "go slow", low mileage, or base-camping and then day-hiking from the base, unless the money is no issue, I doubt you would get your money's worth. There is a vast price difference between a 900-fill high-end brand goose down bag, and a 750 or 650-fill duck down bag (or even synthetic) for about a 1-2 pound weight difference. There are cheaper ways to get rid of 1-2 pounds pack weight, such as carrying less water, recycle light plastic bottled water containers instead of Nalgene bottles, carrying slightly less food, or doing without non-essential gear (such as camp shoes or water crossing shoes). Regardless of the fill-weight of down or source, be sure the bag is well made and fits properly. The high-end expensive stuff does pack down to less volume, so allows a smaller pack, which adds also to some weight savings.
Think of a "sleeping system" rather than individual items, which also include the clothing you plan to sleep in. But, compare total weight, total packed volume and total cost. Comparing total warmth is much harder and very qualitative. Ounce-for-ounce adding 10-degrees to the warmth with a bag is more efficient than adding extra clothing. If you are buying for your wife, be aware that women sleep about 10-degrees colder, and women-specific sleeping bags take that into account. Bags rated for lower temperatures (usually 20-degrees or lower) have a draft collar or equivalent design to keep out drafts if you do not cinch up the hood. If you cannot stand to cinch up a hood, maybe a blanket would suffice (I am not a blanket user but there are plenty here who can add their comments on that).
Everyone is different, but I have not felt the need for a plushier sleeping pad as I age. My old-age aches and pains occur regardless of my sleeping pad, so I still use the same non-plush system I have used for decades, but now take an Advil before sleeping. The sleeping pad for me has more to do with warmth it provides, in fact, I do not like the thicker pads.
If you want to save money, keep an eye out for sales. Pads and bags are very often on sale and you should easily find something about 30% off list price, excluding some brands, like Western Mountaineering, who only sell very high end bags and rarely on sale. There are some good deals on REI-brand bags of moderate quality. For both pad and sleeping bag, be sure you can return the items, and then sleep on your floor at home several nights (leave on all tags and save the packaging) to be sure it works as intended. As much as you lay down on the stuff in the store, spending an entire night on the gear is different.
If you are talking 2-5 years of backpacking in your future, you could also spend the high dollars, get top quality "light and fast" equipment, care for it properly, do your few trips a year, then when you are done, sell it. Better yet, pass it down to the grandkids! Every high-end item I have purchased, even when at a steep discount on sale, has caused my to wince in pain when purchasing, but after many years of use, I never have regretted it.
I am a very cold sleeper, so my "system" is: Western Mountaineering Super Antelope bag (older version before women-specific versions were offered, with 750-fill goose down at 2lb, 14 oz. about 5 to10-degree rating), x-small shoulder to hip Therma-rest Pro-lite self-inflating pad at 8 oz., my backpack below my "pillow" which is a stuff sack with extra clothing, one 2.5x2.5 blue foam pad for feet (for fall or early season I use a 45-inch long blue foam pad). The small blue foam square also is my sit-pad in camp. The blue foam pads are cheap and you can cut them into various widths and lengths. I NEVER take my inflatable sleeping pad out of the tent. I also take a 4-oz down sweater which I sleep in on very cold nights or wrap around my neck. A 1.5 ounce fleece balaclava is added for shoulder seasons.