This link gives some conversion ratios. These are not exact because people differ.

If you had poor metabolism of tramadol in the liver, to its active metabolite, you would have little relief from this drug. Hence your high doses. If that were the case converting directly to morphine or oxycodone SR would not be the ratio shown on this link. (you could overdose on morphine based on artificially high tramadol that wasn't metabolized.)

http://www.gha.net.au/Uploadlibrary/...011-Opioid.pdf

In general costs go this way:
methadone is less expensive dose to dose than morphine SR, morphine is less than oxycodone SR. The oxy products even if generic are the most expensive of the 3. Morphine is a moderately priced opiate.

Availability is also an issue. In the US there can be shortages of oxycodone at times.

In the US pharmacies typically will not give prices of opiates over the phone. You may have to go there in person.

There are other conversion tables on the net. If you Google
"tramadol to morphine conversion doses" you'll find others.