I have to say-if you go too 'cheap' on such equipment, you may well be sorry. For safety AND comfort of horse and driver, decent equipment is SOOOO important! Easy Entry carts should be balanced and NOT too heavy; the best price for a NEW,decent-looking EE I have seen is CTM(www.ctmproducts.com), advertised in MHW at $395 plus tax and shipping. If you are close enough to either of the "national" shows, I would surely check on the possibility of ordering one and then picking it up there(if you were going anyway!)When inquiring, ask such questions as: how much does it weigh, and is the seat adjustable(forward/back)for good balance.
Decent harness is NOT likely to be found on ebay at $99! However, if you will keep it simple, it can still be obtained for around $300, I think. Remember, if you buy quality gear, and take good care of it, if ever you don't need it, there will be a good resale market for it. This is something to think of when contemplating the cost, I believe.
Edited to add: Used EE means a used Easy Entry cart; because they are in such demand, you will seldom see one advertised for sale-people usuallly sell them by word-of-mouth, without having to advertise!
As for the harness you put the link up for--it is next to impossible to know how "good" a harness is if you can't actually see it, "in person", and/or don't know the reputation of the maker. Things like leather quality, quality of stitching/riveting, proper proportions of parts, whether or not the blinder stays have wire in them, the padding/proportions of the harness saddle,and whether it has a tree,etc., are all part of what constitutes overall quality. It would be very helpful to order from someone who themself KNOWS about harness, or sit down with someone who does and can advise you as to what you want/need. Also, a return guarantee, as to fit and suitability to use, would be a BIG plus!