Cheapest guides
It is possible to improve on gw2crafts if you do your research and do a bit of planning based on what you are likely to need in the future. Unless you know the market really well though using your own system based on researching is likely to take you five times as long.
You could hit sites like gw2spidy and gw2craftgold to find value for money recipes and probably get pretty close to breaking even, and in the cases where you lose money you will gain a lesson about how the trading post works. If you just want to get things done quickly however go with gw2crafts. It’s as good as any page out there and getting things done quickly at a reasonable price.
You’ll more than likely do it cheaper than what’s listed on gw2crafts as that site reports everything using sell order prices rather than buy orders.