That is not a sale. That is an FMS notification based on the maximum amount of resources the US is willing to offer to Poland. It also includes the GOTUS estimate for future contractor PBL cost which is very difficult to estimate this out in the future (since Milestone C is just round the corner) and hence is likely a highly conservative estimate.
Following this, there will be long negotiations where Poland will pick and chose their package and then inform then JSF JPO of their schedule and then the JPO will club their orders in when it comes time to place aircraft on order, generally 2-3 years before delivery. The FMS notification is just giving the US Congress an estimate of a pre negotiation top end of what a potential sale could like. It neither means that Poland has “bought” the F-35, nor that they have agreed to go ahead with package as laid out by GOTUS at the present moment.
There is also no way for GOTUS to be certain of what top lime $ the JPO will arrive to an agreement at in the future so these estimates tend to be conservative and reflect the upper limit of a possible future deal. In the past I’ve shared examples of actual negotiated contracts being 30-50% below FMS top line numbers owing to a different package being negotiated or estimates being off as program has had a milestone transition in between FMS notifications and actual contract complete.
Here's an example of this at play -
FMS Notification for SIngapore's purchase of Counterfire AESA radars -
The Defense Security Cooperation Agency notified Congress today of a possible Foreign Military Sale to Singapore of 6 AN/TPQ-53 (V) Counterfire Target Acquisition Radar Systems and associated equipment, parts, training and logistical support for an estimated cost of $179 million. LINK
And the actual contract award, some 4 years later -
The US government has awarded Lockheed Martin a USD63 million firm, fixed-price contract in support of a Foreign Military Sales (FMS) procurement effort of six AN/TPQ-53 counter-fire target acquisition radars destined for Singapore, according to federal contracting documents reviewed by Jane's on 21 August.
The contract – which was signed on 13 April 2017 – includes options that would bring the cumulative value of the order to USD81 million if exercised by the Singapore government. Work on the radar systems is expected to be completed by 13 March 2019, with the US Army Contracting Command-Aberdeen Proving Ground (ACC-APG) in Maryland functioning as the contracting activity...The original DSCA notification of 8 October 2013 for FMS to Singapore involved USD179 million for the purchase of six AN/TPQ-53 radar systems, including all options. The fall in cost to USD81 million reflects a drastic reduction in unit cost of the radar due to full-rate production (FRP). On 30 March 2017, Lockheed Martin was awarded a USD1.59-billion, indefinite delivery/indefinite quantity (ID/IQ) contract for the radar, which included full-rate production of up to 127 radars – including 70 radars for the US Army, 50 for FMS and/or US requirements, and the remaining seven for obsolescence and production. ~ SOURCE - JANE'S International Defense Review 25-Aug-2017
So what changed? FMS notification went through as the system was at a milestone transition i.e. production was ramping up, costs were projected to come down but the FRP contracts had not yet been negotiated with the vendor. In such cases GOTUS is conservative and errs on the side of using a higher number so that their are no surprises to what the Congress has had no objection too.
Having said that, a package for a first time operator (not someone topping up) with GOTUS and contractor support, spares, and a PBL for a block-4 F-35 will probably run 2x of URF and above so a unit price of around $160 Million won't be far fetched once negotiations are complete and they arrive to a package and price that fits their budget.