Well, in terms of power compared to regular Pokemon, the EX cards are a straight upgrade in most cases (even the mediocre EX mons are a little easier to set up and do damage with than non-EX ones, on average). There are comparatively few non-EX attackers that really work well in a fast format like this one, although the numbers of those have been increasing. If you want to build a deck that doesn't rely on EX mons as your primary attackers (those things do get pretty expensive), Night March decks and ones based around Vespiquen AOR (the regular one, not the one with the Ancient Trait) are probably your best bet. I haven't kept up on prices for specific cards because I only play on TCGO (broke college student, wooooo), but I do know most of the things in those decks are fairly inexpensive, with the exception of Shaymin-EX (necessary in pretty much any competitive deck for draw power, and stupidly high-priced). I will note that Night March is better in Expanded than in Standard, though. You can find skeleton lists for both in the Metagame Deck Discussion section and tweak them to suit your needs.
Regarding mons from Burning Spark, Raichu is OK-ish, but it doesn't have the raw power needed to stand up to most modern decks. If you want to use Raichu, better to go for the one from the XY base set and build a deck around that. Stunfisk is in a similar situation, except I don't think there's ever been a competitively viable Stunfisk card. If you're aiming to put this deck together for more casual competitions, then it's a little easier to make a deck from mons taken out of theme decks, but if you're doing this for serious competitive play, the pickings are pretty slim.
