Well the most expensive things aren't necessarily the best items, there are many items that are well-known and actually function better than the more pricey competing products. As well, unless you already know all the prices around town from all or many pet shops, often you won't be getting the best deal if you buy all from 1 store. The large pet chains are convenient, but because of this, they charge a lot more for their products than say, a small privately owned shop somewhere across town. An example of mine was my local PetSmart sold its Rena xP4 filter for 349.99 CDN, but after looking through 5-6 other pet stores around town, I found the same filter in a small shop for 200 CDN, a save of 150 dollars.
Though this
isn't a proven fact, many users of Hagen Fluval brand filters have had trouble with it, including cheap parts that break easily, difficulty maintaining it, and less ease finding replacement parts. Rena brand filters on the other hand, are known to be much more successful in many cases in comparison to Fluval filters, and sometimes the Fluval brand filters even cost more, simply because of its brand name. Just another example I though I'd say about expensive not always being the best.
I haven't had any experience with the water heater and filter you mentioned, so I can't really tell you if they're right or wrong for you, but as far as turtle pellets goes, Tetra
ReptoMin are a popular widely used pellet food for aquatic turtles here, because of their quality and nutritional content. I'd say ReptoMin brand are a well-rounded brand of pellets and are better than other brands for your turtles. If you're looking for the best however, there are two other brands that people have been talking about which are sometimes said to be better than ReptoMin (but are more expensive of course), they are the
Repcal brand turtle pellets and
Mazuri brand turtle pellets. Some say that Mazuri is the best, but it is fairly uncommon and hard to find in shops (I couldn't find that brand where I live).
The Nutrafin Floating Turtle pellets are fine for your turtles, they offer a pretty good amount of nutritional value at a fair price, but in comparison with the above mentioned brands of pellets, they aren't as good. I used this brand of food in the past because of its price, and my turtles seemed to like it well.
If you are determined to buy these items however, before you go out and buy them, remember that a RES turtle grows very quickly (as much as 4 inches its first year), and continues to grow after that, so unless you have a lot of money for continuous upgrades of small increments, it's best to start off as big and best you can, so you don't waste more money on future upgrades if you need to.
One last thing I thought I'd share, again, I have never used the brand of Aquarium Heater and Filter you mentioned, but a popular and quality heater used here by turtle enthusiasts is the
Marineland Visi-Therm Stealth Heater. It only goes up to 250w, but I think in comparison to your 400w heater, it does a great job at maintaining the temperature up to 75 gallon tanks and uses 150w less energy, so unless you have no problem with paying more in your electric bill or have a 200 gallon tank in mind, the Stealth Heaters are a good bet. They are also shatterproof (unless you smash it repeatedly against a table, which I think you wouldn't do), because they are encased in thermoplastic, against glass heaters. They are also fully submersible like the heater you mentioned, and they shut off if out of water. As for the other features you talked about on that 400w heater, they probably won't matter at all (only if you keep exotic fish that must be at an exact temperature).
As for filters, a recommended filter for small tanks is a hang-on style waterfall filter, the
Aquaclear brand filters are good (most that do use this brand go for the Aquaclear 110), they offer very good filtration (even beating out small canister filters at times) at a fair price and save space. If you get a large tank (50 Gallons and up), then it's good to get a large capacity canister filter, they're stronger, and filter out well (I only don't recommend them on small tanks because of the power they have when sucking up water).
Sorry I was uanble to answer your original question at all, this is all I have,

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