Hello, glad you are looking at these great old keyboards! Thanks for posting your message.
You could use keys from an old Model F or Model M keyboard or Unicomp keys but you’d be paying more than $40 for those keys including everything you need (space bar, stabilizer inserts, etc. that are included in the new Model F key sets). The new Model F sets cost about $34 with a keyboard so you wouldn’t really be saving anything, especially if you wanted to maximize resale value of the keyboard with keys included.
These keyboards are costly but they’re designed to last for decades like the originals. They weigh as much as 8 pounds and have a strong metal construction for the case, inner assembly plates, etc. You could easily go through more than $300 worth of other plasticky mechanical keyboards over the life of a new Model F.
If funds are tight, there is also a down payment/payment over time option. The way to do a down payment is to place an order for all the items you want and choose the “other payment” option. Then for your down payment, place a separate order for each deposit/payment using the store item “$1 increments” – at least 50 or 100 at a time. https://www.modelfkeyboards.com/product/other-customizations-in-1-increments/
If shipping is to an address outside the US, one of the down payments you’d pay shipping and for the rest of them you’d choose “free/other shipping” so you are not charged extra for shipping. Shipping is free within the US.