Im tired and by no means an expert, but I love topics like this so heres my 2 cents. xD
Dantooine was basicly temporary prefab structures that allowed them to pick up and leave at a moments notice and Yavin 4's base was built in the ancient massassi temples from the time of Exar K'un. Hoth if I remember correctly that had more time to work on with construction and ice melting equipment, but in the end it was mostly add ons to caves and a previous base. The golan turrets (the white turrets at Hoth) were also 20+ year old technology by the battle of Hoth and not prohibitively expensive, and the older models like the ones on Hoth were known to be aquired by pirates and smugglers for their bases of operation as well. The planetary shield, generator and planetary grade ion cannon were expensive, no doubt, but by the time that Hoth rolled around the Rebellions main funding and source of equipment had begun to move away from "Steal it from the Empire".
"In the past, we'd secretly enjoyed putting down a local insurrection or two, they kept the troops sharp and the Empire feared; but these Rebels were different. They were organized, they were growing, and they were everywhere."
This statement would be a rather fair one considering. A local rebellion is not even in the same league as what became the Rebel Alliance. Where the insurrections would be most likely spontaneous in respose to a show of oppression on a planet or two, the Rebel Alliance promoted an ideal, and the ideal is what drew the creatures from the worlds to join them and bolster their ranks. Defectors with intel, technitians with expertise and experience, soldiers and willing volunteers join together and finally the ideas could be connected between different groups of disidents to form a force that could begin being more then a simple uprising; it could be come a movement with a face, normal people standing up to the empire and even better: making gains.
"Until this battle station is fully operational, we are vulnerable. The Rebel Alliance is too well equipped… They're more dangerous than you realize."- Cassio Tagge
That statement made to high command is not really too suprising, considering the sheer scope of the Empire at that time. With the rebels main source of supplies BBY being stolen Imperial technology from random systems and pooled together, Cassio would most likely bringing this to the moffs because their attention would be just be far above it. Just looking at the amount of manpower, resources and credits it would take to build a victory class star destroyer, not even mentioning a super star destroyer and eventually 2 death stars, why would low end parts and outdated ships be worth their notice? (Hell, Tarkin embezzed enough credits from the death star project, the pride of the Empire mind you, to fund the Maw Installation in complete secrecy for God's sake. =P) Be it arrogance or pride, the notion to the higher ups in the Empire that the billions of credits being dumped into Star destroyers, current R and D projects and the most powerful battlestation ever created were being seriously challenged by stolen hand me down and in some cases obsolete equipment would be laughable. It would be like us considering a group of kids in Missouri who stole their fathers old hand me down bb guns and military gear are a legitimate military force and a threat to our national security. (until one of them shot my eye out with a lucky shot. lol)
TL : DR, Yes, they had high technology and good gear by our standards, but even when you just consider each of those star destroyers above Hoth during the battle held maybe 1-3,000 personnell and cost more to build then the entire Hoth base many times over, they were rather ragtag. <_<