I suppose it depends on how big you want your
collection to be and how many centuries you want to cover.
Low end solidi are in the $500 range these days. Sixth and seventh century solidi from
Justinian I through
Constans II are common. Solidi from Phocas,
Heraclius and
Constans II are quite common.
At the end of the seventh century, the solidi from
Justinian II were the first to include an icon of
Christ. You might find these in the range of $1500 and up. Expect to pay more for a well struck
portrait.
In the eighth century, the solidi of
Constantine V are the most common.
In the ninth century, the solidi of
Basil I are the most common.
In the tenth century, the solidi of
Constantine VII are the most common.
By the time you reach the eleventh century, the
solidus has become the
histamenon -- a broader coin that eventually transitioned to a concave shape. The smaller
tetarteron continued the tradition of flat gold, like the early lightweight solidi. In the eleventh century, the histamena of
Constantine X,
Michael VII,
Romanus IV and
Nicephorus III are the
budget pieces.
Then in the twelfth century, we move into the period of the
hyperpyron. The cheapest ones tend to be the coins of
John II, who was also recognized as a saint in the Orthodox
Church.
The late hyperpyra after the recovery of
Constantinople are another example of
budget Byzantine gold. To me, these lack the
eye appeal of the solidi, but if you are interested in Byzantine
history, these are
part of the story too. In fact, you might even want to add a silver
stavraton to mark the outer bookend of your
collection.