Collecting What's the cheapest way to complete sets?

[Arwen17]

I've gotten back into pokemon card collecting after many, many years. And I managed to accidentally return for Pokemon's 20th anniversary! yay!
I stored all of my old cards for years, so completing those sets via buying singles should be easy.
But what about other old sets? I stopped collecting at the beginning of Gen3, so Gen3-5 is a large gap.
What do you think is the cheapest way to complete sets? The latest Gen6 complete sets on ebay are frequent. Is that the cheapest way for any new set?

Options for collecting old sets:
1. buy singles - buy every single card in the set individually. I usually buy from TrollandToad.
2. buy wholesale booster pack lot - I'm still able to find some reasonably priced wholesale lots for Gen4-6. This gets you all of the uncommon/common cards and a few rares. Then you can sell back the duplicates to TrollandToad for example, but you still have to buy more rares to complete the set, so maybe you're not really saving more money than buying singles in the long run.

Which method do you think is cheapest?
I generally think the older complete sets on ebay are overpriced and you're better off building the set yourself using one of the two methods above. I think only the lastest Gen6 complete sets on ebay are probably reasonably priced.

I don't know if I'll get into online card trading or not, but I'm aware that is an option too.
So far TrollandToad etc has been great about near-mint condition cards. The card doesn't have to be absolutely perfect. I just don't want any obvious played damage.

 

[Athena]

Depends on the set. For example, a BW Base Set you could probably complete with a single booster box. However, a lot of the newer sets have tonnes of RR/SR/UR cards that are difficult to pull. There's also the fact that pull rates have been swingy since about midway through the BW-era, so you can get burned with an unlucky box.

One thing I would recommend would be to stay away from booster pack lots. If you want to buy a large number of packs, sealed booster boxes is better. The problem with the booster pack lots is that they're often weighed. Sites like TNT don't weigh themselves, but they do buy packs from people who do, and those packs will end up in those lots. For sites like eBay, the risk of buying weighed packs is even higher.

If you're feeling lucky, or you like opening packs, I'd suggest buying a single booster box (assuming they're decently prices) and then augmenting with singles for the rest of the cards you don't pull. Some sealed boxes are, however, have raised significantly in price (especially back in the EX era), so this may be prohibitively expensive.

If price is a serious factor, I'd also recommend working either earlier sets first. The reason for this is that the prices of older sets are relatively stable because they are no longer competitive. However, the are many cards now that are worth more solely for their competitive value, so for those you're better off buying to wait until the cards are out of rotation.

In any event, completing sets is always going to be expensive, no matter how you go about it. I wish you luck!