The vast majority of lighting gear, regardless of sticker price, is over-priced for what they are. A $200 'bargain' canbe just as over-priced as a $1000 'higher quality' unit. However, such is life when it comes to lighting. In most cases you get what you pay for, but, like in most things, there are limits and exceptions to that rule.
Some lower-end mfg's and their fans argue (obliquely) that "spendy more is silly/wasting money" while other end argues that "anything less is junk" and round we go. This makes it tough when buying your first modifiers, especially online, to mentally justify X vs Y for +$$$. Toss in online brand loyalties and things get muddy quickly.
OP - some things to consider:
1. You're idea of buying a few higher quality units vs a myriad of cheaper ones is solid. Selling used, lower-end SBs when you've decided to shift brands or shift your modifier sizes around can be costly. A realistic used price, shipped really favors the buyer as even a small SB can entail stiff shipping. Industry 'standard' units that can be used across more than 1 light brand, even with an adapter, will have easier, less painful, resale.
2. Whether or not you think you'll ever use grids, stick to a brand that ALLOWS grid use. Grids themselves are varying degrees of silly-spendy, no need to add to the cost by having to take a hit on swapping out Box A for grid-enabled Box B.
2A. When pricing a box, price the grid as well. Some SB manufacturers have a tendency to have SB sizes that vary from those of their peers. This makes using a cheaper 3rd party grid, say from Photoflex ($), impossible and means the SB maker's own grids ($$), no grids (hello Elinchrom) or custom grids ($$$$$).
3. Silver units are more efficient in light delivery than white. White delivers a softer light and silver typically cost more (price gap varies by manufacturer).
4. Build quality means a lot. Strong/durable fabrics and inner liners and diffuers, steel poles, reliable and solid speed rings, strong corners, velcro (and enough of it) that stays put.
5. Balance ease of opening vs quality of construction. Easy opening but lasts-3-shoots/won't take grids/uneven across the front is about as nice as a units that's built-like-a-brick, even as hell, but is a 10-minute "...who designed this #$%^& nightmare...?" set-up struggle.
6. Don't fixate on the brand from your light manufacturer. Stay brand agnostic. Try, all other things being equal, to pick modifiers that if able, will last you years and across various light brands. No one maker has a perfect line, and no one maker is all junk either.
