To the extent this is a request for product recommendations, it is off-topic because we don't do those here. Any shop can get 27" front repair wheels for that price or under (each), and there are resellers online that have the same kinds of wheels.
There's not a lot of reason to look at anything but standard 100mm-spaced fronts unless, unless you have the notion of making the complete wheels and not just the tubes/tires interchange on to your bike as spares. So if the 27" is a lock, all you really need are 2 27" QR wheels. You could get bolt-on too but then you're carrying a 15mm wrench for no additional benefit. 5/16" axles exist among 27" front wheels; avoid those.
In other words: you want any 27" front (ISO 630) with an axle size of 3/8" or 10mm, and QR or bolt-on (nutted solid spindle) depending on your preference. Resellers are a little all over the place in how they might describe the rim width - you might see "27 x 1-1/4" or you might see something like an outside width in the 22-24mm range, or an inside in the 17-19mm range, all of which indicate the same type of common 27" rim. What you probably want to avoid for this purpose are the narrow 27" rims, which do still exist, that you might see indicated as "27 x 1-1/8" or approximately 20mm outside width, 15mm internal. Presuming you have the 27" size (ISO 630 as found primarily on drop-bar and other road-going bikes sold in the US in the 70s and to a lesser extent the 80s) and not 27.5" (ISO 584), you'll want to make sure to avoid any 27.5" wheels, which is a completely different wheel size.
Most trailer designs that use standard bike wheel take standard 100mm QR/bolt-on axles (10mm dropouts). A typical one would be something like an early Burley, where it's a square frame with 2 other tubes running down the middle, and then some dropouts made of angle aluminum bolted on.
Giving up the inherent strength and lower center of mass that small wheels offer just to get tube, tire, and possibly spoke interchangeability is very questionable. This is especially true if you're doing a seatpost hitch (easier to fabricate but far more prone to tipping). The weight factor of needing to carry an additional tube more or less pays for itself since 20" wheels would be lighter.
