I'm going to compare the Murchison Widefield Array (MWA) to the Green Banks Telescope (GBT) just to pick two rather big projects.
The first phase of the MWA featured
256 128 tiles and cost A$ 51 million.
About the MWA: http://www.mwatelescope.org/telescope
It saw first light in 2013.
edit: the first phase comprised 128 tiles only but I could not find out if the 51 million were the price for the first or the first and second phase.
The GBT cost US$95 million and saw first light in 2003.
To make it compare better: US$ saw an inflation of 1.27 within 10a making a total of USD 120 million. AUD is 0.68 USD bringing down the cost of the MWA to USD 34.5 million.
both telescopes got a lot of upgrades later.
It is difficult to compare but the GBT has a much higher receiver area while the MWA has a vastly greater baseline. They serve different purposes. From this point of view they don't seem to differ in an order of magnitude in pricing.
But the question was about "cheap" parts. Here the costs of the MWA are broken down (page 8). Only 12% of the total costs are related to the front end (i.e. antenna and beam steering electronics), the rest goes in equal parts to the infrastructure and the back end. Considering that in a design like the MWA a lot of signal processing is already part of the design it might even be cheaper in total when considering costs for later upgrades.