Dried herbs really do only last around six months, certainly no longer than a year. They're generally easy to get in small quantities, though.
Spices are trickier. They'll generally last rather longer, but the time will vary. If the spice is used for the colour and/or heat (e.g. turmeric, chilli) it will generally last much, much longer than one used for its smell and/or taste. Whole spices last much, much longer than pre-ground; I generally buy whole spices from asian stores, they sell them in much larger amounts for the same prices as supermarkets; and use a coffee mill to grind the right amount just before cooking (and keep a separate one for coffee!).
If kept in the dark, in a dry, clean, airtight glass container, spices and dried herbs will certainly not become health hazards, and should not pick up unpleasant tastes or odours. The strong-tasting / strong-smelling ones will, however, lose taste and smell, eventually almost completely; since that is the whole point of using them, you might as well not bother once they're off.
Agree that planted herbs are great but you say you've tried that. I kill about 1/4 to 1/2 what I plant, but those that live thrive and get bigger. After a big push just over a year ago I have an endless supply of thyme, rosemary, lemon balm and a dozen sage varieties. I do think it helps if you use them sparingly in their first season so they can get established.
I don't know where you live, but if in a city or anywhere near a foreign enclave you might find herbs at an Asian market or other international market much cheaper. It's $4-6 for tiny plastic container of cilantro or mint at my local grocery, for instance, but at the Vietnamese and Chinese markets it's usually 0.50 - $1.25 for a big bunch.
To make any leafy green herb last longer in the short term wrap them in a wet paper towel and put that in a plastic bag.
You can freeze what you don't use in small ice cube trays for easy serving / use later. I especially like this for basil and mint. You can also buy pre-frozen herbs.
You can also dry them - air dry upside down, accelerate by drying them in the oven on low (very low) or use a food dehydrator.
Best Answer
In order to preserve your custard applies I would suggest canning them since you have already frezing it. It does lose it's freshness to an extent, however, the shelf life would last longer.
Canning is also a good method as is can use vacuum sealed packaging which restricts air into the packaging which is what causes micro-organism growth an multiplication.